Over the last ~15 years, I've DD'd all generations of Miatas ;)
Lemme give you a rundown:
1. 1991 - This was a HPDE car that was driven very regularly because it was hella fun. No PS, no AC. It had Tokico dampers and Eibach springs. In the spring/fall/winter it was a decent DD. Wind noise was strong, and there was a rattle here and there. Overall pretty OK and did a trek to Oklahoma City from Austin and wasn't uncomfortable.
2. 2008 PRHT - The best DD of them all, IMO. I had the GT model and added Bilstein HD damper and Eibach springs with FatCat bumpstops. Rode great, pretty quiet inside, no complaints at all. Did some New Mexico and Las Vegas runs in this one, great trips and didn't get out of the car complaining.
3. 2004 Mazdaspeed - Stock suspension was harsh and not all that comfortable, even still, did a Monterey, CA trip in it without too many complaints. Road/Wind noise is lower than the '91, but not as quiet as the '08. I've since got an OEM hard top on it and replaced the suspension with Flyin' Miata VMaxx Classics. Good DD now, but still not '08 level, but close. I'm going to pack the space beneath the parcel shelf this weekend to see if I can get some of the road noise down just because it's cheap and easy.
4. 2016 - Better than the '04 w/ soft top, noisier than '04 with HT. Done two Monterey, CA trips in this without much complaint. Interior room is VERY improved over all previous years (I also lost 100lbs, so that helps, lol, but even before that it was better). It's nice to have bluetooth and now CarPlay. I've got the RoadsterSport springs (300fr/200r) and it's still a good ride but not as good as the '08.
If you have specific questions of any of the above models, lemme know.