The underbelt pulley sounds like a good idea, I may try one after Jake plays with it a bit more. I liked an ECU flash on my base boxster. Only picks up about 10 hp or so, but if its a good flash, remapping the throttle response coupled with little more hp made the car seem more responsive.
Also ditto on saving weight, it can start out being a be a cheap way to make the car more responsive. Lose the spare tire and put in a lightweight battery and you are 50 lbs lighter. Put in GT3 seats and aftermarket exhaust and you are another 50+ lbs lighter. Put in a lightweight flywheel and you are another 15 lbs lighter of rotating mass and you get the added bonus of being able to worry about when the undamped harmonics are going to rattle your engine to pieces
Ed