The ITR is basically a 200 HP Civic, so there really aren't a lot of problems. Most problems are owner-induced.

As far as tuneability, I'd certainly aim for buying a car that's as close to completely OEM as possible, or a car whose "improvements" are easily understood (intake, header, exhaust). I'm not sure what else you'd mean by tuneability. I have a cheap Hondata system on mine and it works very well, infinitely tuneable.