my next thing will be to refinish the stock rims if i can find a place in the NYC area. i dont drive my car that aggresively so i am not sure what / when i will do more performance upgrades. but you are right - the springs could be one of the biggest bangs for your buck that you can do to your car.
The only time I've installed the IAP springs was on a '69 Spider, so don't know if this applies to 'modern' Spiders, but the front springs went Bang! (at separate times) when I lowered the car to the ground. They are larger in diameter then teh stock springs, so apparently had to settle in. I was afraid they might bang once on the road, but were no problem.