I looked for a Boxster for a loooong time in the $25,000 range, thinking the same as you do, older faster S or newer more refined and slower base, until I got this:-
'04 S, 40,000 mls, 1 owner (no lease), triple black, Porsche certified with full Porsche warranty until 2014 or 100,000 mls, totally flawless, all service records, first owner is anal about his Porsche, he traded for a '10 S, $ 23,000 with 1.9% Porsche financing..... hard to beat IMHO. Heck, they put new HTZ 3 tires, brakes etc on before I got it.
Point is there are so many Boxsters out there for much less $ than mine but this one is just like a new car, never has seen rain or snow. I just waited for the "right" and "clean" ride!
Good luck!