ive actually seen thease engines go to 400,000 miles without having it overhauled... as long as the engines been well maintained you should be fine... as far as the rest of the car... well bushings wear out and the suspension gets kinda loose.. the tranny's are pretty durable.. if you were to get the car id change all the oil in the diff and tranny.. check to see if the engines still got good compression.. and drive the car.. see how it feels.. for that amound of miles i wouldnt pay more than $1500 for it...

 

I've had my 280zx for a few years now. I'm up to 210,000 miles. It still runs great and has good compression. The syncros in the transmission (mainly 2nd gear) are going out, but it still works pretty good. Shifts solid and stays in gear with hardly any noise at all.
I do need to do some maintenance to it though. I've got slightly higher compression than stock and it pings a bit with low octain fuel. That tells me I've got a good amount of carbon buildup on the valves. I also have lost some low end torque over the last couple years which is probably due to a retarded cam. That is fixed by replacing the timing chain. I can fix all that for $100 and one day's work if I find the time.

also, the suspension is getting a little soft and the differential mounts seem to be loose. Typical stuff

 

Bleach,
Go buy some GM Top Engine Clean and run it through one of you vacuum lines toward the middle of your intake. Buy the large can and follow the directions on the back. This will take care of the carbon build up you have and you should notice an improvement in acceleration.

As for high mileage Zs, my daily driver has 242k on the odometer and is running great for the time being after a brief episode with a plugged up catalytic converter. The transmission is making temendous noise at this mileage in all gears so I'll be swapping in my spare T-5 soon.