Hi Dave!
Fellow countryman
'
I'm more or less in the same situation as you are. I'm currently a boxster 987 owner and will trade that for a 997 within the next upcoming months. I have decided to go for the 997 C2S based on the fact that I did regret from day 1 that i didn't get the S-version in the boxster.
For resale value the S is a better buy if you anyway will add upp options like 19":s, pasm, bi-xenon etc. That equipment alone is half the way to a S.
If you buy an expensive car like a 997 you don't want to sit in your new dream-car the day it arrives and think "should I've ordered the S?" and everytime you'll see an "S" on the road you'll know that it's a little bit faster than your own car
... If you know that you wont ask yourself this question, then fine.. go for the base-model
..
Since the step-up to a 997TT and GT3 is so much more money, this is not even in the ball-park, but stepping up from a base to a S for 10K EUR is more justified IMO and will make your ownership more pleasant
Cheers / Lukas