one thing you better check when buying an RX-8 is your own local mazda dealer network. the RX-8 has a rotary engine, which is a far different engine from the typical piston engine, and in some places, mechanics experienced in servicing the rotary engine is pretty rare. at 45k miles i'd make sure i have maintenance people around the area that i live in - 22.5k miles per year ain't a joke, that's a lot to run in a year. plus, the 1.3L engine displacement doesn't translate into good fuel mileage, again because it's a rotary. it does about the same as a 2.5L or 3.0L piston engine in terms of fuel mileage.
other than that, mazda's are typically reliable, provided you care for it.