Personally, I'd keep all of the cars, but I'd list them in a different way. I'd class [Make] [Model] [Engine] as "a car" and then allow players to choose their trim after that:
So the car list would say:
1. Mazda, MX-5/Roadster/Miata NA, 1.6
2. Mazda, MX-5/Roadster/Miata NA, 1.8
3. Mazda, MX-5/Roadster/Miata NB, 1.6
4. Mazda, MX-5/Roadster/Miata NB, 1.8
5. Mazda, MX-5/Miata NC Roadster, 1.8
6. Mazda, MX-5/Miata NC Roadster, 2.0
7. Mazda, MX-5/Miata NC Coupe, 1.8
8. Mazda, MX-5/Miata NC Coupe, 2.0
And so on, and the players could choose from further submenus:
2. Mazda, MX-5/Roadster/Miata NA 1.8:
Miata (LHD)
'93, Limited Edition '93, M-Edition '94, M-Edition '95, M-Edition '96, M-Edition '97, STO '97
Eunos Roadster (RHD)
'93, S-Limited '93, J-Limited '94, G-Limited '95, R-Limited '95, RS-Limited '95, V-Special '96, VR-Limited I '96, VR-Limited II '96, SR-Limited '97, VR-Special '98
MX-5 (LHD)
'93, SE '93, Gleneagles '95, California '95, Monaco '96, Merlot '96, Dakar '97, Monza '97, Harvard '97, Classic '97, Berkeley '98
MX-5 (RHD)
'93, SE '93, Gleneagles '95, California '95, Monaco '96, Merlot '96, Dakar '97, Monza '97, Harvard '97, Classic '97, Berkeley '98
So the car list would say the MX-5/Miata/Roadster NA 1.8 was one car, but really players got forty cars to choose from...
You could add in generational facelifts (NB.5, NC.5, NC.75) to the eight listed cars and they could even include racing cars. So they'd promise eight cars, but really players would get up to a hundred. They'd have to be real and different though - there's no such thing as an MX-5 or Miata VR-Limited, so while duplicating the car for regional name differences is at least reasonable, giving us nonexistent trims calls the usefulness into question.
Do it the other way round and players get annoyed that there's a hundred listed cars but really only eight...