Depends if these are really spreadsheets or specialist "applications" made of excel formulas by "non-technical" users. If you are really looking at large file

Depends if these are really spreadsheets or specialist "applications" made of excel formulas by "non-technical" users. If you are really looking at large file based table data and are similarly unable to persuade the author to produce a sensible format, I've had a good time with VisiData