Shocks

Mostly it harms the handling and safety. Remember: the job of the suspension is to keep the tires on the road so that you can keep the rear end from trying to pass the front end. IOW, if the tires aren't on the road, you can't control of your car.

If you have different damping rates on left/right, the car isn't going to want to go straight while braking or accellerating on bumpy surfaces. Once the shocks are gone, it's also going to be very jittery and hard to control on bumpy curves.

You're already seeing it--there hasn't been anything left for the past

Worst case, in an emergency your stopping distance may be about 30% longer than with good shocks. Or worse, if you're not good at threshold braking.

good news is that quality aftermarket shocks are a buy-once proposition on the miata. They will out live your precious lil hotrod. KYB AGX are excellent and lots of people swear by the Koni's, both are adjustable.

Chris