Module to read Excel as if it was just XML. Needs work (e.g. some cleanup after data is read).

Excel.psm1

<#
    List taken from SO answer:
    http://stackoverflow.com/questions/4730152/what-indicates-an-office-open-xml-cell-contains-a-date-time-value
#>

$ExCellStyles = @{
    0 = 'General'
    1 = '0'
    2 = '0.00'
    3 = '#,##0'
    4 = '#,##0.00'

    9 = '0%'
    10 = '0.00%'
    11 = '0.00E+00'
    12 = '# ?/?'
    13 = '# ??/??'
    14 = 'mm-dd-yy'
    15 = 'd-mmm-yy'
    16 = 'd-mmm'
    17 = 'mmm-yy'
    18 = 'h:mm AM/PM'
    19 = 'h:mm:ss AM/PM'
    20 = 'h:mm'
    21 = 'h:mm:ss'
    22 = 'm/d/yy h:mm'

    37 = '#,##0 (#,##0)'
    38 = '#,##0 [Red](#,##0)'
    39 = '#,##0.00(#,##0.00)'
    40 = '#,##0.00[Red](#,##0.00)'

    44 = '_("$"* #,##0.00_)_("$"* \(#,##0.00\)_("$"* "-"??_)_(@_)'
    45 = 'mm:ss'
    46 = '[h]:mm:ss'
    47 = 'mmss.0'
    48 = '##0.0E+0'
    49 = '@'

    27 = '[$-404]e/m/d'
    30 = 'm/d/yy'
    36 = '[$-404]e/m/d'
    50 = '[$-404]e/m/d'
    57 = '[$-404]e/m/d'

    59 = 't0'
    60 = 't0.00'
    61 = 't#,##0'
    62 = 't#,##0.00'
    67 = 't0%'
    68 = 't0.00%'
    69 = 't# ?/?'
    70 = 't# ??/??'
}


function Get-ExcelData {
[CmdletBinding()]
param(
    $Path,
    $sheet,
    $HeaderRow = 1
)
    $fullName = Resolve-Path -Path $Path | ForEach-Object { $_.ProviderPath }
    $zip = [System.IO.Path]::GetTempFileName() | 
        Rename-Item -NewName { $_ -replace 'tmp$', 'zip' } -PassThru
    Get-Item -LiteralPath $fullName | Copy-Item -Destination $zip.FullName
    $folder = Split-Path -Leaf $fullName

    $shell = New-Object -ComObject Shell.Application
    $source = $shell.Namespace($zip.FullName)

    $destinationFolder = (mkdir -Path ([System.IO.Path]::GetTempPath() + $folder) -Force).FullName
    Remove-Item -Path $destinationFolder\* -Force -Recurse

    $destination = $shell.Namespace($destinationFolder)
    $destination.CopyHere($source.Items())

    $xmlNs = @{ 
        Namespace = @{
            d = 'http://schemas.openxmlformats.org/spreadsheetml/2006/main'     
        }
    }

    $sheets = Select-Xml -Path "$destinationFolder\xl\workbook.xml" -XPath //d:sheets @xmlNs | 
        ForEach-Object { 
            $_.Node.sheet 
        } | Where-Object { 
            $_.Name -match $sheet 
        } | ForEach-Object { 
            $_.id -replace 'rId(\d+)', 'sheet$1.xml' 
        }
    $Strings = Select-Xml -Path "$destinationFolder\xl\sharedStrings.xml" -XPath //d:sst @xmlNs |
        foreach { $_.Node }
#    $Strings
    $addedStyles = @{}
    Select-Xml -Path "$destinationFolder\xl\styles.xml" -XPath //d:numFmts @xmlNs |
        foreach { $_.Node.numFmt } | foreach {
            $addedStyles[[int]$_.numFmtId] = $_.formatCode
        }

    $styles = $Script:ExCellStyles + $addedStyles

    $formats = @(Select-Xml -Path "$destinationFolder\xl\styles.xml" @xmlNs -XPath //d:cellXfs | 
        foreach { $_.Node.xf } | foreach { $styles[[int]$_.numFmtId]})

    foreach ($sheet in $sheets) { 
        $data = Select-Xml -Path "$destinationFolder\xl\worksheets\$sheet" -XPath //d:sheetData @xmlNs |
            foreach { $_.Node.row } | foreach { $_.c } | foreach {
                New-Object PSObject -Property @{
                    Column = $_.r -replace '\d'
                    Row = $_.r -replace '\D'
                    Value = if ($_.t) {
                        $Strings.Si[$_.v].t
                    } else {
                        $_.v
                    }
                    Style = if ($_.s) {
                        $formats[$_.s]
                    } else {
                        'General'
                    }

                }
            }

        $headers = @{} 
        $data | Where-Object { 
                $_.Row -eq $HeaderRow 
            } | ForEach-Object { 
                if ($_.Value) {
                    $headers[$_.Column] = $_.Value 
                }
            }

        $rows = $data | Where-Object { 
                $_.Row -gt $HeaderRow 
            } | Group-Object -Property Row -AsHashTable 
        
        foreach ($row in $($rows.Keys | Sort-Object { [int]$_ })) {
            $properties = @{}
            $noValue = $true
            foreach ($Key in $headers.Keys) {
                $Cell = $rows[$row] | Where-Object { $_.Column -eq $Key }
                if ($value = $Cell.Value) {
                    $value = $value | 
                        Add-Member -MemberType NoteProperty -Value $Cell.Style -Name Style -PassThru
                }
                $properties[$headers[$Key]] = $value
                if ($value) {
                    $noValue = $false
                }
            }
            if (-not $noValue) {
                New-Object PSObject -Property $properties
            }
        }
    }
}