Make sure you don't get one that has been road racing or Autocrossing. Those are likely beat to hell.
Miata's are some of the most road raced and autocrossed cars on the planet. Autocross doesn't hurt a car one bit. Stick in 2nd or 3rd gear the entire time, go 20-40mph.
Anyway, I daily drive a 2004 mazdaspeed miata. Before that, a 99 miata.
The cars are very well built and last a long time. Residual value (resale) is typically very high. Trunk space is small but manageable, I usually can fit a whole shopping cart of groceries in and still have room for the FNP45 bag.
All miata's are small, 2 seat, 4 cylinder, rear-wheel drive, convertibles. They were offered as 5 and 6spd manual, and automatic (but why would anyone?....) For all generations, lots of aftermarket support for changing suspension, stiffening frame, adding turbos, bigger race tires, installing roll bars, replacing seats, just about anything. This is a cheap racers sports car, and so there is a decent size industry for everything for it.
These cars are all about lightness for performance. So small, small, small is the rule of the day.
The manual convertible is so easy to work, I can do it at a red light from the driver seat. And I have done this quite often.
There are 3 generations of miata body style/drivetrain.
Late 80's to 97 called an "NA".
Mostly 1.6L [BP engine family], some later years optioned a 1.8L. Offered as a 5-speed manual. Lightest generation of the bunch. Soft suspension, but immensely fun. Very cheap, which makes it a good candidate for modding and hooning.
99 to 06 called "NB"
All are 1.8L [BP engine family], 5spd and 6spd. Big body style change from the NA. A little more expensive. 04 and 05 had a very limited mazdaspeed version with a factory turbo. Spring rates are still soft, but damping is pretty aggressive to give it an aggressive feel. Body roll is minimal. I prefer this generation's body style.
06 to current called "NC"
All are new 2.0L [new engine family: MZR]. Another body style change. Newest = most expensive. All are naturally aspirated, but this gen makes decent power from the 2L. I hear the suspension has stiffened and refined to something more modern. First generation to have powered convertible option.
Love, love, love this car. The feel of the steering is so awesome. The steering and handling is awesome, that speed limits feel meaningless. 75mph might as well be 35. The braking capacity is immense, and the shifter feels smooth and clutch feels natural.
The NA and NB naturally aspirated versions are not fast by any means. I'm talking early 90's V6 mustang slow, I'm talking minivan slow. But they out handle anything short of a Porsche on curves, stock. With gentle streetable mods (slightly stiffer suspension, and sticky tires) they are an absolute beast through any corner, easily pushing past over 1g. All generations use a double wishbone suspension on all four corners, no struts here. Which also makes for easier damper and spring upgrades.
Here is a after market turbo'd NA chasing down/passing a Viper at Thunderhill.
http://youtu.be/v0GrTGopcW4?t=48sThe engine and trans,
while stock, are 200k+ mi reliable. They are designed with the budget racer in mind, so Mazda builds a LOT of engineering margin into these cars. The NA and NB engine families were built/designed with turbocharging in mind. They provided oil ports and low compression pistons and forged cranks on this BP engine family. All the engines are 4v/DOHC, with timing belt. Since it is a longitudinal engine, belt changes are a cake walk. Turbocharging is a very popular mod because it is so easy and makes the car really come alive. I would not be afraid of a used after market turbocharged version, if done by somebody that knows what they are doing. Otherwise, get a mazdaspeed with factory turbo and same engine.