WWW.miatanet.com is your friend. If you get a first generation car beware of the short crank issue on 90/91 cars. If you get a 99 model beware of a main bearing problem with some of these cars.
Really decent cars and one will probably be my njext automotive purchase....I'd rather buy a Cooper S However I can buy a great used Miata for $4500-8500 and a decent used Cooper S will set me back at least 15 grand...but that's beside the point.
Make shure you unzip the rear window if you put down the top. The interior is a little dark and gloomy with the top up and they do have a nice blind spt with the top up. They make a replacement convertible top with a larger rear window area if you don't like the blind spot, but expect to pay for a top and an install (prob 600-800 to get it done right ) if you want this.
Watch for rust around the rocker panels on older first gen cars. Easily fixed, but a problem none the less.
Good luck and keep us posted. The Miata is one of the coolest cars of the last 20 years IMHO. You might also check out WWW.Specmiata.com for info on the Miata only racing series run by the SCCA nad NASA. Also, there is a pro series called the MX5-Cup that runs current generation Miatas.
Also, check the timing belt. Needs done every 60,000 miles, might as well do the water pump when you do this. It is about a $450 service if you pay someone. All Mzda motors are non-interference so you won't destroy the motor if it breaks, but the car will stop moving.
Glad to have at least one other Miata lover here.
Chris