Low90 I can give you another data point on a 90. I bought mine in 12/04 from the orig owner. 7800 miles on the odo, both tops, pizza box, dealership paper work for the sale, no original sticker but the one w/the pizza box. Car had three stone nicks up front and some scratches on the radio/center waterfall bezel(the one that is NLA). I paid 24,900.00. I feel it was a fair price but towards the high side of "fair".
Hindsight says I should have bought a car with more miles and mods from a gear head second owner. I would have saved myself a bunch of $ as all the "common issues" would have been addressed for me. Consider that as you look because if the car sat and you want to drive it alot, you will get stuck buying all the parts to address the "common issues". That is not an insignificant amount of $v and work if you wrench it yourself....if you don't wrench yourself then add that cost in as well. Oh I forgot, mine had the OEM/BG tires complete with BG air in them....plenty o tread left, great, right? NOT...they were hard as rocks, no rot, but not tiresyou want to drive on. There's another $1,000.00 out of my pocket.
The reality, as I see it with my 90, is injectors, hydraulic systems don't like sittin and then being called back to work, and the stero system...speakers and head unit repairs. Just the gaskets to do the usual housekeeping on an injector swap out are a coupla hundred dollars. Bear all this in mind.
Moral of the story from MHO is a 90 Z with some miles from a gear head second owner trumps a garage queen any day. You get all the issues solved for about $0.50 on the dollar and if you're lucky ya get mods that up the power too for next to nothing!
JMHO.
Tom