You are arguing semantics... Do you think that the current 997TT is just a heavy car?
You are right about comparing the same weight of AWD VS non AWD cars, I am used to thinking about it in terms of a similar model with or without.
But your STi only had better acceleration in the wet, correct? Or did AWD somehow help cornering and braking in the wet as well? If you pulled out the rear diff and driveshaft, and retuned the suspension (if needed) to accomodate the weight change, do you think it would corner and brake better or worse?
I do think the current Porsches are just heavy cars. To me, a 997TT is an awesome GT car, but I would prefer a GT3, which is significantly lighter. (although still on the heavy side) Cheaper too, also...RWD. I also would bet that your STi stomped the Exige because of better software. The Exige is the car I would really want if I had the means.
You also correctly point out that you and I have different ideas about street driving, but even when I'm keeping it legal/sane I feel every pound*, and exactly how much traction there is...I always like less of both. Feel is really important to me, and most people just want to feel like they are fast, or beat the next guy at the stoplight.
Alex, I think you should be worried about consequences in FWD cars...first of all, some of them are particularly nasty when they do let go, and secondly because if you are driving fast without always knowing exactly what will happen, before it does, based on your inputs, then you are asking for a surprise someday. If I were you, I would get the STi, and then spend some money on training, or go auto-Xing until you have a feel for the limits of the car and yourself. You'll be safer, have a blast doing it, and driving will be more fun for the rest of your life.
*OK, every 50 pounds, but still.