I like this mod a lot! Even if my taste is biased owning a 1994 Miata. Does handle pretty good, but it acts pretty oddly under two circumstances.
1 is the flywheel weight (?) The car seems to rev up and down really quickly, definitely find a way to slow that down.*
2 is with an open differential. This may be the game rather than the car though but this also may be tied to the flywheel.
Some other suggestions include configurations like a hardtop, R-package aero, and pop-ups, and different wheels, something similar to the daisies or hollow spokes.