First and most important mod = Driver Mod.
I'd say hold off on any serious mods and spend the money on track days/autox events (and the tires you'll burn through).
Another thing to keep in mind is classing structure for any competitive event you plan on doing. With SCCA autox, it's very easy to mod your car into a class you don't want to be in.
On a side note where in Ohio are you? If you're anywhere near Toledo come out to one of the SCCA autox regional events (
HOME).