I've now had my '98 Z34 for 5 years. I've had few issues with her. She now has over 160,000 miles on the original engine and transmission and she runs smoothly. Surprisingly, the gas mileage has gotten better with age! I average around 24 MPG (21 around town; 28 on the Interstate). All of the accessories have held up well. One of the few complaints I have is the quality of the center console--there is a plastic coating that tends to rub off and the hinges for the console storage lid broke. Mechanically, this car has done pretty well. I've had some seemingly unique issues: transmission solenoid failed at 40K mi.; plenum warped at 130K (plastic cover on top of engine). Overall, I am VERY happy with my '98 Z34!
The leather seats are so comfortable! That was one of the major selling points to me. I'm a salesman, so I spend LOTS of time in my car! Great stereo. Power is good. A/C blows cold every time! Good tires. Great trunk space. Auto headlights are awesome! What did I do before w/o dual climate zones?!
Most of the improvements I would suggest have already been made: more gauges; supercharged option; more unique styling.