I've always wanted a supercoupe myself. 94/95 5 speed only though... As stated, the Ford 3.8 is a nightmare.... Until you put a decent set of heads on it. Not only that, but you will need to ring the heads as to prevent head gasket eating. That is an expensive process in itself. As said, they aren't the fastest, but they can be modified to be running pretty quick for a respectable price(I think). If you want to see what some guys do, check out the sccoa(super coupe club of america), or if you don't mind people being childish, the thunderbird underground.
The V8 models are actually slower than the supercoupes. The old 302'* are like the new 281'* that they put in from 94 to 97. Not enough torque for such a heavy car. The 281'* have very limited space to work in in the engine bay. However, you can still swap in a GT engine, a Cobra engine, or a 330 truck engine. Some guys with the earlier models and the 302 setup have swapped in 351'* and stroked them out. It'* sad how much smaller the pushrod engines seem compared to the OHC engines. One thing I will say for certain, the 281'* are reliable. The 94/95'* had bad valve seals, so they'd start burning oil somewhere around 80k. Mine'* been burning oil for a loooooong time, and it'* still got 183k on it. Never had the heads off for any reason, only took the intake off to modify it a little.
The 96/97 T-Birds with the V8'* had a problem with the instake manifolds cracking under WOT shifts. They was corrected and a new intake with an aluminum crossover coolant pipe(the part that was cracking) has proven to be the solution. I could tell you all about what you can do with the 94 to 97 T-Birds, since that'* what I've studied the most. One thing to remember, and it'* the best part. The 8.8 gears are easy to change out for lower or higher ratio'*
Plus independant rear suspension is a good start if you are looking to modify for handling.
Bottom line, the supercoupes are no doubt fun, can be made quick, but need to be modified so they don't eat headgaskets.
The 302'* have waaaay too little motor, but engine mods are pretty cheap, and you can switch it up to get more displacement.
281'* can be modified all over the place. Pretty much, any engine part that fits a Mustang can be adapted to fit a T-Bird, with the exception of exhaust manifolds/headers. And we all know that Mustangs have a biiiiig aftermarket.
The 2.3L Turbo coupes are neat little cars, considering the output of that engine almost matches the factory 281 from 94/95.
I'm sure I've missed tons of info, but I'm at work.