The best Miata to supe up (IMHO) would be a 96 or newer.
It has a knock sensor and the air flow metering system is better for super charger (or turbo charging).
I know the 1.6 and 1.8 had piston squirters, which insures piston skirt oiling. I am not sure about the other engines. Both the 1.6 and 1.8 have windage trays and other custom parts to squeak out a few more horses.
With some work (blue printing the engine, turbo/super charging) they can produce 250 HP.
If that is not enough get the kit (or have it done for you) for a Monster Miata. The 302 engine can be built to operate in the 500 HP range all day long.
Me, I will just stick with my 90 Miata. A few more horses would be fun. But anything over 200 would take the fun out of it.