I think for now I'd save the money and see what I may need/want once you've got some events done this season. You know, things to bring the handling that much closer to your ultimate preference.

Though, if you really want to spend the money, you can't go wrong with safety equipment. Maybe a new helmet, or [for autocross only!] a harness bar and 4/5 point belts. Just remember that racing harnesses are not street legal, and could be lethal anyways without a roll cage along with them, though autocrosses normally don't get enough speed for that to be much concern.