Man, I love S14's, but that's one that's always escaped me! Years ago, another friend of mine had a '95 with a Redtop SR20 in it and that thing was criminally fun to drive making ~275whp or so. Some cars are just cursed, though, I believe in that.
I'm not sure I could disagree more emphatically with that second part, though - All the new Mercedes, Audi, BMW stuff with turbos have massive intake/exhaust/tune potential. VW's and Mini Cooper S's too.
Rewriting the PCM to enjoy those changes voids the warranty, though, so a lot of folks aren't willing to cross that line.
The new 'Supra' is included in that thanks to it being 99% BMW, The GT-R is a GT-R of course, but the Nissan Q50/Q60 with the new VR30DDTT direct injected TT V6 is showing a lot of promise with tuning as well. That's begging the question as to why the hell Nissan haven't stuffed that engine in a 370Z with a 6MT behind it, because I'd seriously think about buying a 370Z 6MT new if it had a potent TT V6 under the hood.
Similarly, the Newer Honda K-motor stuff is fantastic if you can deal with FWD and the Civic Type R is showing promise as well.
The only issue I have with the newer stuff has to do with what I'm comfortable spending on a car I'm messing with and potentially blowing up - which is why I like the older, cheaper stuff.