How to save xls{,x} as csv file so that formulas show as text?

I just tested it and it's a lot easier than I thought to get output like the 2nd case you specified.

Do the following:

1. Input all your data/formulas
2. Select the Show Formulas button (via Formulas > Formula Auditing in Excel 2007)
3. Save As filetype CSV(MS-DOS)
4. Open resultant file in Notepad to verify.

I'll play around with it for a bit more to see if I can get it to pare down the formulas like you mentioned in case 3.

The same applies for LibreOffice Calc (Version: 6.0.6.2):

1. Show formulas (Ctrl+`),
2. Select "Save as" (Shift+Ctrl+S),
3. Select "Text CSV (.csv)" from the list
4. Tick "Save cell formulas instead of calculated values"