Some older Excel files may not have a specific DPI set for printing quality under page setup. The result is that the pages look strange under print preview and when printed. This happens because Excel choses the lowest DPI for the printer.
The virtual printer has a setting for 1 DPI where most printers start at 300 DPI. Because the 1 DPI option is selected automatically by Excel the result is clearly poor.
You can fix this by changing the print quality under page setup. Manually select 300 DPI or higher for good results. Page setup settings are saved with the rest of the workbook.
If this is a problem for a large number of files then you can use an alternative solution to fix the problem. Locate the printer's PPD file and remove the low resolutions. That way Excel cannot select them.