>also it makes a hole lot more sense to buy a 500$ set of wheels for a 1500$ car than paying how much i got the car for i wheels.
Then why not get a decent, lightweight set of wheels from a proven manufacturer like Konig or Enkei? Unsprung weight makes all the difference in a Miata, and the lower rotational inertia sure does help.
>2. If you are not racing, there is no reason to upgrade.
See above: unsprung weight and rotational inertia are literally the devil in terms of vehicle dynamics.