re: Which SEC school has contributed the most to the conference?

In recent history I'd say Florida has contributed the most overall. It is a large school with very solid academics and top-shelf athletic programs. At least over the last 20 years or so it is easily the top because it does everything well.

Historically it is a bit trickier. Vandy is clearly the academic heavyweight. It is one of the most prestigious schools in the entire south. Alabama put the SEC on the map for football (although several other programs have historically been strong, I can admit Bama is the best historically). Kentucky of course owns the SEC in basketball.