simply "stripping" a car doesn't make a car more balanced with less weight and feel.
i'm also a bit confused with this comparo, but i can say for sure whether stripped or not track tuned or not the M3 has so much potential than the 370Z.
the Engine itself is far better than the one in 370Z.
i never felt 370Z as a good "80~90% track dedicated" car.
For that money and the major track tool purpose, i'd just get a used lotus elise (not exige...the price too high), better brakes and better tires and just run miles and miles on track driving.