I'm halfway through the 20 years book. It's a bit of a hotchpotch but still a good read. Helps you appreciate even more why the MX-5 is such a brilliant and important car. Doesn't have much on the Japanese side of the engineering work for the NA, but I've got that covered with the Roadster book. I've quickly flicked through that book and all those glorious engineering drawings, CAD schematics and graphs have got me "aroused".
Isn't that an NA8 on the cover of the Roadster book? Sacrilege! Should have been an NA6!
BTW, here's the chapter list for the 20 Years book. A bit cryptic but gives you a rough idea of what's in it.
1. GIs and MGs (background to the appeal of roadsters in the USA)
2. Roadster reborn (detailed coverage of Bob Hall's pitch and the prototype development by the American team)
3. Birthing pains (comments from Tom Matano and Mark Jordan on the Japanese build development)
4. The dream comes true (launch at the Chicago Motor Show)
5. Crunch time (testing in the US)
6. A rewarding experience (derivation of the "Miata" name)
7. Love at first delight (press and public reactions to the NA6)
8. Red, white, or blue, and then British racing green (various colours and special editions for NA)
9. Even better the second time around
10. Pace car for a roadster revolution
11. Third time: Still a charmer
12. The monster and other mutations
13. Off to the races
14. Miatamania
15. The next 20 years
16. Encore