Take a look at the brakes (pads and rotors wear out fairly quick on these cars), roof mechanism (if it's a power top, put it up and down...it should be a smooth motion), rattles coming from the rear of the car (near where the top would be stored in the down position), and believe it or not, the gas gauge (Z3s also shared the same problem).
These cars have bulletproof engines and perform very well. To be honest, I'd go 3.0 if you can...after driving both, there's simply no comparison. The extra 30 some horsepower difference is more than noticeable.
If you're interested, my car is for sale. Here's the thread:
http://www.zpost.com/forums/showthre...38#post1866338