i'd agree to a degree with what charizma said, alot of the zed's that come in aren't treated right. but you can't rule out the 300zx all together just because a few are bad.
you're looking for an NA 2+2.... the australian delivered 300zx's were all NA 2+2's. Benefits of buying an aussie delivered model are that you're more than likely to get genuine k's. my NA z32 is an import, odo reads 145,000km... considering my zed is now 17 years old i find it hard to believe that it's only averaged 8500km per year, obviously it's been wound back. You're less likely to get this with aussie delivered zeds, and you can always ask for service history to back it up.
Power wise the NA zed puts out 160kw and around 270nm stock. with regards to basic bolt on mods i'd say it may even respond better to the pod filter, exhaust, catback etc compared to the r33... not 100% sure on this though but i'd guess the extra capacity would help... don't flame me if i'm wrong though. 0-100km in roughly 7ish seconds and good for about a 15sec pass at the drags.
common misconception is that zeds overheat, engine out to change the seats lol etc... admittedly yes the engine bay is cramped, even in NA form. that's what you get with a quad cam v6 engine but i've never heard of a well maintained zed overheating. the cooling system needs to be well maintained on any car but on a zed, with the cramped engine bay you really need to ensure that your cooling system is pressure tested and is in good nic. before i started my mods, the first thing i did was get the radiator flushed and rodded, replaced the thermostat and waterpump (part of the 100k service- which is another thing you should do when you buy a zed... unless you can prove it's been done, do the 100k service) and i also replaced my upper and lower radiator hoses. my cooling system is perfect and i've done deca through SAU and a few other track days and i've never overheated, temperature stays rock solid. so the myth that the z32's are overheaters is just bs.
if your budget is 15-16k you'll get a very nice zed, probably mid 90's. standard features on my '90 z32 are things like electric/folding mirrors, electric seats, electric windows, climate control. a mid '90's zed will have things like ABS and airbags standard... remember these cars sold for 80k plus... so i've got features in my '90 z32 that my friends vt commo doesn't have lol
best advice for you is to join up to www.aus300zx.com if you are interested, you can read and ask for advice. the guys there are very helpful, just like the guys on this forum. we all share a passion for the cars so we're all willing to advise anyone.
admittedly, i am quite biased to the z32... i've owned mine now for just over a year. thing that attracted me to the z32 was the fact that you don't see too many people driving them, if you do join aus300zx.com, you'll see we only have about 4000 members. very small compared to SAU or NS. also if you sit in another '90's nissan you'll notice that the Z32 was a very different place to sit inside, it was a much more expensive car at the time and it shows. also IMO, even after 17 years i think it still looks damn fine. only thing that makes it look old is the stock front bar but if you replace that with something like the '99 300zx front bar it completely updates it.
aftermarket parts market is good for the 300zx. not as good as the skyline because after all these years people are starting to forget about the z32, there's more money to be made making bodykits for civics. but you're in sydney so you've got Unique Autosports (www.nismo.com.au) . There's also places like www.ttzed.com, www.perthzperformance.com, www.cazracing.com.au. and with the dollar being so good atm, check out www.conceptzperformance.com , www.z1motorsports.com and www.specialtyz.com . also the z32 has support from nissan australia because it was australian delivered so you can get parts from them too but all the suppliers i listed above can often do better prices than nissan.
my advice would be to test drive each of the cars you're interested in. if you do need a pre purchase inspection on a zed, give Unique Autosports a call. Also try Autotech as they deal with zeds also.
hope this is of assistance to you, sorry about the long post but.
sandeep