Hi Andrew,
A regular, rather expensive service on the NSX is the Timingbelt & Water pump.
Which, according to my service manual says should be replaced every 90,000 miles / 72 months.
Every NSX known to man has bad window regulators and bad speaker amplifiers.
The radiator usually starts to leak around the endtanks, the ugly coolant bottle can leak/crack at the seem, and the rad hoses particularly between the engine and the firewall tend to leak/crack (due to thermal and motion fatigue!).
There is a fan in the cockpit that usually makes a lot of noise.
People tend to go through clutches (a bit of a pricey affair).
Some other electrical gremlins with the main relay/ignition switch/fuel pump resistor. These go bad, and can cause the car to not start.
The valvetrains are very noisey (they sound like sewing machines). Newer springs solve this problem.
All of the above is a matter of when, not if. But they're all known, fixable issues!
These cars are bulletproof (I've got over 120,000 miles, many others have more).
Go for it if the car seems in decent condition! (Don't be scared by the above list).
Oh, and the black NSXs got an extra 10 hp from the factory.
Happy hunting!
Lucas