Background: Bought mine as an NA in 2000. It was converted to a twin turbo in 2006. I modifed my NA with a variety of bolt-ons to 206rwhp/188rwtq. I took it to the strip once as an NA and ran a disgusting 15.5 or so. I've been AutoX'ing since 2002 with the car.
The Z32 is a rather interesting car - but it's a love/hate relationship depending on your goals, budget, patience and ability (and space) to turn a wrench. The NA models are becoming more and more affordable as the years roll on, especially with higher mileage. Finding one in good condition isn't impossible, but you will find a lot more in need of serious TLC than not.
As 1fynzx said, the major mistake I've seen MANY owners make over the years is to buy an NA while wanting a TT. That will be more costly over time as you try and make the NA faster, all the while getting nowhere. On the topic of NA vs. TT, finding a TT that needs some basic maintenance is much more of a payoff. You will never make the NA as fast as a stock+ TT, if even a stock one - unless of course you pour TONS of money into it.
Reliability? It's an over-engineered GT car released in 1989 and the newest one you will find state-side is going to be 13 years old. They can be reliable, but once you start modifying them (as with any car) they have a better chance of showing worn parts.
They're great cars - but aren't as easy to work on due to cramped engine bays (TT especially). Parts aren't super cheap, but they aren't in the German part category either. Plenty of aftermarket support - some that is still being developed by a few performance shops for the twin turbo model. They handle well with fresh stock components - and even better with upgraded parts. The brakes are easily the weak point of the car.
There are many people rocking them at the strip, road course and AutoX. They shine at the first two the most, being designed for road course-type driving first and foremost. The car can be built to do any of the three (I AutoX mine), but long and twisty is where it is really home imho. Wondering what some of the faster ones are running at the strip: http://z32racing.com/
I've seen a couple NA models breaching the 300rwhp mark (usually with nitrous or stroked motors). I've seen TT models hitting anywhere between 260rwhp - 1100 rwhp.
I could go on and on... and on, but I won't yet. This forum is the only one you will need: http://www.twinturbo.net
Here is some additional reading:
http://twinturbo.net/nissan/300zx/FAQ/FAQpages/differences.html
http://twinturbo.net/nissan/300zx/FAQ/FAQpages/usedpurchasing.html
http://twinturbo.net/nissan/300zx/FAQ/FAQpages/natott.html
http://twinturbo.net/net/viewmsg.aspx?forum=technical&msg_id=952659
More questions - shoot. Although any and all questions regarding this car from technical to aesthetic can be almost surely answered by SilverTwin in detail.