Steam Broadcast Chat Cleaner - cleans up the chat of any Steam Broadcast, massively increasing the conversation quality. Works on Dota 2's Watch page as well. Requires Greasemonkey (Firefox) or Tampermonkey (Chrome). Screenshots: http://i.imgur.com/7qEfM9B.png, http://i.imgur.com/PHW4TbK.png - Click "Raw" to install.

SteamBroadcastChatCleaner.user.js

// ==UserScript==
// @name         Steam Broadcast Chat Cleaner
// @namespace    http://jzhang.net/
// @version      3.1.1
// @description  Cleans up Steam Broadcast chat
// @author       waylaidwanderer
// @include      http://steamcommunity.com/broadcast/watch/*
// @require      //code.jquery.com/jquery-1.11.3.min.js
// @downloadURL  https://gist.github.com/waylaidwanderer/6bb095e0731ef41d49dc/raw/SteamBroadcastChatCleaner.user.js
// @updateURL    https://gist.github.com/waylaidwanderer/6bb095e0731ef41d49dc/raw/SteamBroadcastChatCleaner.user.js
// @grant        GM_getValue
// @grant        GM_setValue
// @grant        GM_addStyle
// ==/UserScript==

(function(){
    function GM_wait()
    {
        if (typeof jQuery != 'undefined') {
            letsJQuery(jQuery);
        } else if (typeof unsafeWindow.jQuery == 'undefined') {
            window.setTimeout(GM_wait,100);
        }
        else {
            unsafeWindow.jQuery(function() { letsJQuery(unsafeWindow.jQuery); });
        }
    }
    GM_wait();

    function letsJQuery($)
    {
        var $body = $('body');

        var englishOnly = GM_getValue("englishOnly", false);
        var noEmoticonsOnly = GM_getValue("noEmoticonsOnly", true);
        var noEmoticonsOnlyPercent = GM_getValue("noEmoticonsOnlyPercent", 50);
        var noAllCaps = GM_getValue("noAllCaps", true);
        var noAllCapsPercent = GM_getValue("noAllCapsPercent", 80);
        var noRepeatedText = GM_getValue("noRepeatedText", true);
        var noRepeatedTextMaxRepeats = GM_getValue("noRepeatedTextMaxRepeats", 2);
        var noShortMessages = GM_getValue("noShortMessages", true);
        var noShortMessagesMinLength = GM_getValue("noShortMessagesMinLength", 3);
        var noRepeatedMessages = GM_getValue("noRepeatedMessages", true);
        var noRepeatedMessagesMaxRepeats = GM_getValue("noRepeatedMessagesMaxRepeats", 1);
        var noRepeatedMessagesMuteUser = GM_getValue("noRepeatedMessagesMuteUser", false);
        var showMessageRemoved = GM_getValue("showMessageRemoved", false);
        var enableWordFilter = GM_getValue("enableWordFilter", false);
        var wordFilter = GM_getValue("wordFilter", "").split(",");

        $(".EmoticonContainer").after("<div class=\"EmoticonContainer ChatSettings\" style=\"cursor: pointer;\"><span style=\"opacity: 0.4; display: inline-block; height: 22px; width: 22px; margin-top: 4px; vertical-align: middle; background: url('data:image/png;base64,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') no-repeat center;\">&nbsp;</span></div>");

        var settingsClass = (window.location != window.parent.location) ? "iframe" : "no-iframe";
        $body.append ('\
            <div id="chat-settings" class="'+settingsClass+'">\
                <form>\
                    <div class="form-group">\
                        <input type="checkbox" id="englishOnly"'+(englishOnly ? " checked" : "")+'>\
                        <label for="englishOnly">Hide Non-English Messages (also hides emoticons which use Unicode characters like <span style=\"display: inline-block;\">( ͡° ͜ʖ ͡°))</span></label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noEmoticonsOnly"'+(noEmoticonsOnly ? " checked" : "")+'>\
                        <label for="noEmoticonsOnly">Hide Emoticons-Only Messages</label>\
                        <br>\
                        <input type="number" id="noEmoticonsOnlyPercent" min="0" max="100" style="margin: 5px auto 5px 25px;" value="'+noEmoticonsOnlyPercent+'">\
                        <label for="noEmoticonsOnlyPercent">% of message that has to be emoticons (emoticons count as 1.5 characters)</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noAllCaps"'+(noAllCaps ? " checked" : "")+'>\
                        <label for="noAllCaps">Hide ALL-CAPS Messages</label>\
                        <br>\
                        <input type="number" id="noAllCapsPercent" min="0" max="100" style="margin: 5px auto 5px 25px;" value="'+noAllCapsPercent+'">\
                        <label for="noAllCapsPercent">% of message that has to be ALL CAPS</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noRepeatedText"'+(noRepeatedText ? " checked" : "")+'>\
                        <label for="noRepeatedText">Hide Repeated-Characters/Words Messages</label>\
                        <br>\
                        <input type="number" id="noRepeatedTextMaxRepeats" min="1" style="margin: 5px auto 5px 25px;" value="'+noRepeatedTextMaxRepeats+'">\
                        <label for="noRepeatedTextMaxRepeats">Maximum # of repeated occurrences</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noShortMessages"'+(noShortMessages ? " checked" : "")+'>\
                        <label for="noShortMessages">Hide Short Messages</label>\
                        <br>\
                        <input type="number" id="noShortMessagesMinLength" min="0" style="margin: 5px auto 5px 25px;" value="'+noShortMessagesMinLength+'">\
                        <label for="noShortMessagesMinLength">Minimum # of characters</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noRepeatedMessages"'+(noRepeatedMessages ? " checked" : "")+'>\
                        <label for="noRepeatedMessages">Hide Repeated Messages</label>\
                        <br>\
                        <input type="number" id="noRepeatedMessagesMaxRepeats" min="0" style="margin: 5px auto 5px 25px;" value="'+noRepeatedMessagesMaxRepeats+'">\
                        <label for="noRepeatedMessagesMaxRepeats"># of repeated messages before action</label>\
                        <br>\
                        <input type="checkbox" id="noRepeatedMessagesMuteUser" style="margin: 5px auto 5px 25px;"'+(noRepeatedMessagesMuteUser ? " checked" : "")+'>\
                        <label for="noRepeatedMessagesMuteUser">Also mute user</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="enableWordFilter"'+(enableWordFilter ? " checked" : "")+'>\
                        <label for="enableWordFilter">Enable word filter</label>\
                        <br>\
                        <input type="text" id="wordFilter" style="margin: 5px auto 5px 25px;" value="'+wordFilter+'">\
                        <label for="wordFilter">Comma-delimited list of words to filter (case insensitive). Prepend word with * for case-sensitive word (e.g. "*LoL")</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="showMessageRemoved"'+(showMessageRemoved ? " checked" : "")+'>\
                        <label for="showMessageRemoved">Show "&lt;message deleted&gt;" instead of hiding message</label>\
                    </div>\
                    <div class="buttons">\
                        <a href="#" class="close ChatSend">Close</a>\
                        <a href="#" class="save ChatSend">Save</a>\
                    </div>\
                </form>\
            </div>\
        ');

        $body.on('mouseenter', '.ChatSettings span', function() {
            $(this).css('opacity', 1);
        });

        $body.on('mouseleave', '.ChatSettings span', function() {
            $(this).css('opacity', 0.4);
        });

        $body.on('click', '#chat-settings .close', function() {
            $("#chat-settings").hide();
        });

        $body.on('click', '#chat-settings .save', function() {
            GM_setValue("englishOnly", $("#englishOnly").is(':checked'));
            GM_setValue("noEmoticonsOnly", $("#noEmoticonsOnly").is(':checked'));
            GM_setValue("noEmoticonsOnlyPercent", $("#noEmoticonsOnlyPercent").val());
            GM_setValue("noAllCaps", $("#noAllCaps").is(':checked'));
            GM_setValue("noAllCapsPercent", $("#noAllCapsPercent").val());
            GM_setValue("noRepeatedText", $("#noRepeatedText").is(':checked'));
            GM_setValue("noRepeatedTextMaxRepeats", $("#noRepeatedTextMaxRepeats").val());
            GM_setValue("noShortMessages", $("#noShortMessages").is(':checked'));
            GM_setValue("noShortMessagesMinLength", $("#noShortMessagesMinLength").val());
            GM_setValue("noRepeatedMessages", $("#noRepeatedMessages").is(':checked'));
            GM_setValue("noRepeatedMessagesMaxRepeats", $("#noRepeatedMessagesMaxRepeats").val());
            GM_setValue("noRepeatedMessagesMuteUser", $("#noRepeatedMessagesMuteUser").is(':checked'));
            GM_setValue("showMessageRemoved", $("#showMessageRemoved").is(':checked'));
            GM_setValue("enableWordFilter", $("#enableWordFilter").is(':checked'));
            GM_setValue("wordFilter", $("#wordFilter").val());
            englishOnly = GM_getValue("englishOnly", true);
            noEmoticonsOnly = GM_getValue("noEmoticonsOnly", true);
            noEmoticonsOnlyPercent = GM_getValue("noEmoticonsOnlyPercent", true);
            noAllCaps = GM_getValue("noAllCaps", true);
            noAllCapsPercent = GM_getValue("noAllCapsPercent", 80);
            noRepeatedText = GM_getValue("noRepeatedText", true);
            noRepeatedTextMaxRepeats = GM_getValue("noRepeatedTextMaxRepeats", 2);
            noShortMessages = GM_getValue("noShortMessages", true);
            noShortMessagesMinLength = GM_getValue("noShortMessagesMinLength", 3);
            noRepeatedMessages = GM_getValue("noRepeatedMessages", true);
            noRepeatedMessagesMaxRepeats = GM_getValue("noRepeatedMessagesMaxRepeats", 2);
            noRepeatedMessagesMuteUser = GM_getValue("noRepeatedMessagesMuteUser", false);
            showMessageRemoved = GM_getValue("showMessageRemoved", false);
            enableWordFilter = GM_getValue("enableWordFilter", false);
            wordFilter = GM_getValue("wordFilter", "").split(",");
            $("#chat-settings").hide();
        });

        $body.on('click', '.ChatSettings', function() {
            $("#chat-settings").toggle();
        });

        $body.on('click', '.message-removed a', function() {
            $(this).hide();
            $(this).parent().find('span').show();
        });

        waitForKeyElements("#ChatMessages div.ChatMessage", processMessages);
        var repeatedMessages = [];

        function processMessages(jNode) {
            var remove = false;
            var message = jNode.find(".tmplChatMessage").text();

            var originalMessage = jNode.find(".tmplChatMessage").html();
            message = message.replace(/<img[^>]*>/g,"").trim();

            if (noEmoticonsOnly && !remove) {
                if (message == "") {
                    remove = true;
                } else {
                    var div = "<div>" + originalMessage + "</div>";
                    var numEmoticons = $(div).find('img').length;
                    if (parseFloat(numEmoticons * 1.5 / (message.length + numEmoticons) * 100) >= noEmoticonsOnlyPercent) {
                        remove = true;
                    }
                }
            }
            if (englishOnly && !remove) {
                var regex = /[^\x00-\x7F]+/;
                if (message.match(regex)) {
                    remove = true;
                }
            }
            if (noShortMessages && !remove) {
                if (message.length < noShortMessagesMinLength) {
                    remove = true;
                }
            }
            if (noAllCaps && !remove) {
                var numCaps = 0;
                var tmpMessage = message.replace(/\s+/g, '');
                for (var i = 0; i < tmpMessage.length; i++) {
                    var char = tmpMessage[i];
                    if (char == char.toUpperCase()) {
                        numCaps++;
                    }
                }
                if (parseFloat(numCaps / tmpMessage.length * 100) >= noAllCapsPercent) {
                    remove = true;
                }
            }
            if (noRepeatedText && !remove) {
                var tmpMessage = message.replace(/\s+/g, '').toLowerCase();

                var repeats = [];
                var lengthToCheck = 1;
                while (lengthToCheck < tmpMessage.length) {
                    var chunks = chunkString(tmpMessage, lengthToCheck);
                    for (var i = 0; i < chunks.length; i++) {
                        var nextChunk = (typeof chunks[i+1] === 'undefined') ? "" : chunks[i+1];
                        if (chunks[i] == nextChunk) {
                            var foundRepeat = false;
                            for (var j = 0; j < repeats.length; j++) {
                                var repeatData = repeats[j];
                                if (repeatData.value == chunks[i]) {
                                    repeatData.numRepeats++;
                                    foundRepeat = true;
                                    if (repeatData.numRepeats > noRepeatedTextMaxRepeats) {
                                        remove = true;
                                    }
                                    break;
                                }
                            }
                            if (remove) {
                                break;
                            } else if (!foundRepeat) {
                                var data = {
                                    value: chunks[i],
                                    numRepeats: 1
                                };
                                repeats.push(data);
                            }
                        }
                    }
                    lengthToCheck++;
                }
            }
            if (noRepeatedMessages && !remove) {
                var steamId = jNode.attr("data-steamid");
                var found = false;
                for (var i = 0; i < repeatedMessages.length; i++) {
                    var user = repeatedMessages[i];
                    if (!user.muted) {
                        if (user.steamId == steamId) {
                            found = true;
                            if (user.lastMessage == message) {
                                user.numRepeats++;
                                if (user.numRepeats > noRepeatedMessagesMaxRepeats) {
                                    if (noRepeatedMessagesMuteUser) {
                                        user.muted = true;
                                        var personaName = jNode.find(".tmplChatName").text();
                                        BroadcastWatch.GetChat().MuteUser(steamId, personaName);
                                    }
                                    remove = true;
                                }
                            } else {
                                user.lastMessage = message;
                            }
                            break;
                        }
                    }
                }
                if (!found) {
                    var data = {
                        steamId: steamId,
                        lastMessage: message,
                        numRepeats: 0,
                        muted: false
                    };
                    repeatedMessages.push(data);
                }
            }
            if (enableWordFilter && !remove) {
                var words = message.replace(/[.,-\/#!$%\^&\*;:{}=\-_`~()]/g,'').split(" ");
                for (var i = 0; i < words.length; i++) {
                    var word = words[i].trim();
                    if (word != "") {
                        for (var j = 0; j < wordFilter.length; j++) {
                            var filterWord = wordFilter[j].trim();
                            var caseSensitive = filterWord.charAt(0) == "*";
                            if (caseSensitive) {
                                filterWord = filterWord.replace("*", "");
                                if (filterWord == word) {
                                    remove = true;
                                    break;
                                }
                            } else {
                                if (filterWord.toLowerCase() == word.toLowerCase()) {
                                    remove = true;
                                    break;
                                }
                            }
                        }
                        if (remove) {
                            break;
                        }
                    }
                }
            }

            if (remove) {
                if (showMessageRemoved) {
                    jNode.find(".tmplChatMessage").html("<span class=\"message-removed\"><a href=\"#\">&lt;message deleted&gt;</a><span style=\"display: none;\">"+originalMessage+"</span></span>");
                } else {
                    var chat = BroadcastWatch.GetChat();
                    jNode.remove();
                    chat.TrimChat();
                    chat.UpdateScroll();
                }
            }
        }

        function chunkString(str, length) {
            return str.match(new RegExp('.{1,' + length + '}', 'g'));
        }

        function waitForKeyElements (
            selectorTxt,    /* Required: The jQuery selector string that
             specifies the desired element(s).
             */
            actionFunction, /* Required: The code to run when elements are
             found. It is passed a jNode to the matched
             element.
             */
            bWaitOnce,      /* Optional: If false, will continue to scan for
             new elements even after the first match is
             found.
             */
            iframeSelector  /* Optional: If set, identifies the iframe to
             search.
             */
        ) {
            var targetNodes, btargetsFound;

            if (typeof iframeSelector == "undefined")
                targetNodes     = $(selectorTxt);
            else
                targetNodes     = $(iframeSelector).contents ()
                    .find (selectorTxt);

            if (targetNodes  &&  targetNodes.length > 0) {
                btargetsFound   = true;
                /*--- Found target node(s).  Go through each and act if they
                 are new.
                 */
                targetNodes.each ( function () {
                    var jThis        = $(this);
                    var alreadyFound = jThis.data ('alreadyFound')  ||  false;

                    if (!alreadyFound) {
                        //--- Call the payload function.
                        var cancelFound     = actionFunction (jThis);
                        if (cancelFound)
                            btargetsFound   = false;
                        else
                            jThis.data ('alreadyFound', true);
                    }
                } );
            }
            else {
                btargetsFound   = false;
            }

            //--- Get the timer-control variable for this selector.
            var controlObj      = waitForKeyElements.controlObj  ||  {};
            var controlKey      = selectorTxt.replace (/[^\w]/g, "_");
            var timeControl     = controlObj [controlKey];

            //--- Now set or clear the timer as appropriate.
            if (btargetsFound  &&  bWaitOnce  &&  timeControl) {
                //--- The only condition where we need to clear the timer.
                clearInterval (timeControl);
                delete controlObj [controlKey]
            }
            else {
                //--- Set a timer, if needed.
                if ( ! timeControl) {
                    timeControl = setInterval ( function () {
                            waitForKeyElements (    selectorTxt,
                                actionFunction,
                                bWaitOnce,
                                iframeSelector
                            );
                        },
                        0
                    );
                    controlObj [controlKey] = timeControl;
                }
            }
            waitForKeyElements.controlObj   = controlObj;
        }

        GM_addStyle("\
            #chat-settings {\
                display: none;\
                border: 3px double black;\
                z-index: 777;\
                border: 1px solid #4c4c4c;\
                background-color: #292929;\
            }\
            #chat-settings.no-iframe {\
                height: 492px;\
                width: 476px;\
                position: fixed;\
                top: 50%;\
                left: 50%;\
                margin-left:-238px;\
                margin-top:-273px;\
                padding: 2em;\
            }\
            #chat-settings.iframe {\
                height: 100%;\
                position: absolute;\
                padding: 1em;\
                top: 0;\
                bottom: 0;\
                left: 0;\
                right: 0;\
            }\
            #chat-settings .form-group {\
                padding-bottom: 5px;\
            }\
            #chat-settings input[type=number] {\
                width: 45px;\
            }\
            #chat-settings .buttons {\
                padding-top: 20px;\
            }\
            #chat-settings .ChatSend {\
                padding: 5px;\
            }\
        " );
    }
})();

Still working for future TI6 broadcasts!