I've had a 2007 since new as a three season daily driver for 100,000 miles now, and it's been to over 30-40 track days since 2010. As I've got it set up, it's a very balanced track car with adequate power and great brakes.
It's been quite reliable, the only real non-wear item I've had to deal with was a belt tensioner, but those just seem to be a 60-70,000 mile wear item.
Track related wear items have included lots of tires, pads and rotors, a front strut bearing, front ball joints and bushings, rear control arm bushings, and the front are rear passenger side wheel bearings. Oil analysis still shows the engine as healthy.
Consumables aren't Miata costs, but not bad, especially if you compare them to the M Z4 coupe. I run 17" wheels, which saves about $80 a corner in tires, and an entire set of rotors runs under $300 shipped, as opposed to almost that much a piece for the M. Hawk DTC-60 track pads are still pricey though!
I've got a six speed, and those are relatively rare. I think the numbers are something like roughly 800 in North America-- there's more for the M versions, that all had manual transmissions.
Most of the underhood service items are easy to access-- at least on the top side. There's a lot of room under that long hood.
It's also kind of neat to be able to get more than 30 mpg on highway cruises to and from the track.
PS-- Just to be that guy, the coupe is an E86.