It seems like all the major points have already been covered above, but I would like to add my $.02 about one point. If you can't afford to rebuild your engine if necessary, you shouldn't put any modification on your car which will void the warranty on your engine.
I have seen people who have blown an engine with just a chip and no power adder. I have also seen several people who's engine blew just a few miles after they installed a supercharger, even with a good tune and safe a/f ratio. There is no way to know if you have a weaker engine than normal or stronger engine than normal, and if you put a mod on there that voids your warranty and then have engine problems, they are not going to repair it. You will end up paying for it. So keep that in mind before you decide to do modifications that void the warranty on your engine.