I've just bought mine and I guess it depends on what you are looking to achive with the car. If your gonna mod it well then persoanly I'd look for one thats already done. Much cheaper trust me. I've spent 10k on my car already since I got it and If I had of bought it with these mods it would have saved at least 3-4 I reckon.
Noise was one of my biggest concerns when I was test driving. Heard things like scraping and whining in the rear end which is not a good sign. Also look for things like overspray on parts of the car and areas that look newerolder than the rest. Signs that it may have been repaired.
Persoanly I have a cooler, ECU, boost controller, frontdumpo pipe, hi-flo cat, cat-back exhaust, Bride Brix seat and rims. They were my first concern to get the most out of what I already had.
Hope that helps.