Well this has been a long time coming, but Signup Ahead can finally(!) import from an Excel spreadsheet directly. Go ahead and upload those XLS and XLSX files, no need to convert to CSV first! It also supports LibreOffice/OpenOffice ODS files.
Also, the CSV export column format has changed slightly. The Start column used to have both date and time. Now there is a new Date column which holds the date, and Start is time only. Not to worry, the old format is still supported on upload.