My daily driver is an '03 Miata. Except for tires and a timing-belt change nobody has worked on the car except me...not that its really needed anything. I've done brakes, a new top, re-upholstered the seats, new speakers, all the oils, plugs, filters - all very easy to deal with and not a challenge.
Mechanically there are some minor differences between the original "NA" Miata and the second-gen "NB"s but size-wise they're similar. If anything that's my only complaint: the NA/NB Miatas (perhaps the NB more so) are slightly small for the driver and the way you sit in the car is a little annoying. If the seat went back another inch and if the seats were made so it was more like MGB, then it would be a little better. Jumping out of an MGB into the Miata is like jumping out of a comfortable recliner into a high-back kitchen chair - sometimes it feels like you're sitting up on top of the car rather than "in" the car. That's just an observation, not really a complaint.
The current "NC" version (of which there are some good deals to be had if you want to get newer) is totally different. Where the NA and NB were very closely related, the NC is new. Mechanically the suspension is different, cast aluminum parts replaced stamped-steel/welded parts. The rear-end of the RX8 was taken and put on the MX5 which is supposedly more advanced and better. The earlier cars had an aluminum hood but steel trunk, the NC has both an aluminum hood and trunk. My complaint about sitting "on top" of the car was addressed too: you tend to sit down in the NC, more like the MGB is.
I've left the best part of this rambling for the end: I've never owned a vehicle that has put me into part of an owners "community" more than the Miata - and that includes my MG. When another Miata passes me the owner will almost always wave or flash his lights, and when I've been behind another Miata the owner will usually wave when he or I turn.
A couple of months ago a lady stopped me in a Disney World parking lot to ask me a bunch of questions about my Miata - turned out she just bought one just like mine and was excited as a little kid about it. On my trip to Maine in October the lady that runs the hotel owns an NA Miata and wouldn't have anything else - when a guest arrived in a red '07 NC she and I both looked it over really closely and we all talked about Miatas.
Point is - for a lot of owners these aren't a "cute little convertible", they're cars that the owners just love. Often that attitude shows and it adds to the fun. And that's the bottom line: they're fun.