Process the Unity generated Xcode project to allow dSYM generation on Release but keeping the distribution size the same, only tested in a clean generated project.

gistfile1.cs

// Adjust dSYM generation
var xcodeProjectPath = Path.Combine(xcodeProjectDir, "Unity-iPhone.xcodeproj");
var pbxPath = Path.Combine(xcodeProjectPath, "project.pbxproj");

var sb = new System.Text.StringBuilder();

var xcodeProjectLines = File.ReadAllLines(pbxPath);
foreach (var line in xcodeProjectLines)
{
	// Remove from OTHER_LDFLAGS
	if (line.Contains("-Wl,-S,-x"))
		continue;

	// iOS Default when not present is dwarf-with-dsym
	if (line.Contains("DEBUG_INFORMATION_FORMAT"))
	{
		// Replace line to stripping on postprocess deployment flags
		sb.AppendLine("\t\t\t\tDEPLOYMENT_POSTPROCESSING = YES;");
		sb.AppendLine("\t\t\t\tSEPARATE_STRIP = YES;");
		sb.AppendLine("\t\t\t\tSTRIP_INSTALLED_PRODUCT = YES;");
		continue;
	}

	// Defaults to Yes
	if (line.Contains("COPY_PHASE_STRIP"))
		continue;

	// Defaults to Yes
	if (line.Contains("GCC_GENERATE_DEBUGGING_SYMBOLS"))
		continue;

	sb.AppendLine(line);
}

File.WriteAllText(pbxPath, sb.ToString());

I forked this and wrapped it in a build post-processor. Just drop https://gist.github.com/tenpn/f8da1b7df7352a1d50ff into your project and future builds will have crash info enabled.