I would go with lighter 17s and see if there's any more weight savings. Get your camber set and suspension tuned so you lose less speed in turns.
Without FI or E85, I don't think you're going to get any more power beyond headers and a good tune. More powerful cars will make time on you in the straights. Just try to beat the Miatas and forget about the Porsches
A 2L NA is only going to do so much.