my sc3 has 205k miles, stock w58 tranny (my car's window sticker clearly says 5spd), and it's still running strong. The only problem I see with sc's is that b/c it's a lexus, the bushings are super soft == higher possibility to tear at higher mileages. But, suspension and steering rack, etc can be replaced with polyurethane (prothane, r2, daizen, etc). Another thing is the rear main seal may develop leaks so you'd have to drop the tranny to get to it to stop oil leaks. parts-wise, it comes out to 35$ or something, but labor will require a lot more.
b/c sc's are getting pretty old, smog could be a problem but as long as you just make sure to clean out the EGR valve before you go in for testing, it should pass with no problems.
also, mileage blows. I used to get ~22mpg (95% freeway driving) on 17" rpf1s, but now that i've gone up to 18", i think Ive settled around 20-21mpg.
I can't really say much about s14's since I've never owned one, just wanted to let you know of a few things that would probably pop up during the ownership of an sc.
