Most cars mentioned that are 4 door are so, in some cases it does matter, other cases it dosen't. Somtimes it's just a simple case of prefrence or maybe more weight, the better at higher speed. I'm not too big on 4 door sedans though, save the Lan evo IV (I got too addicted to that car in GT1...and the Evo III...Initial D lately is also thanks to that...) and also the Tom's Chaser (the standard chaser was also good in GT1, I think it would be the same for GT2 as well...). I'm curious to the 4 door Skyline cars, I think I tried one or two in GT2, they seamed okay, I may want to try more if and when I get GT4 and what 4 door cars are out there in GT3. But again, it could just simply be prefrence.
As for JW31, it does, at the same time it does not, I dunno what you exaclty mean, my only guess is that you're wondering if it REALLY matter's to a car's performace if it's a 2 door or a 4 door. Well, if there is a Lancer evo coupe i don't know about it and the Sedan seams fine enough, but again, it depends.
Well, that's my say on it anywho, sorry if I sound like a really drawn out echo and such...
till later.