Get a CAI and tune. Then some gears and an LSD. Those will be parts that will give you some good gains and shouldn't do too much to void your warranty and are somewhat easy to uninstall. The dealership shouldn't be able to tell whether you put in an LSD and gears and you can take off a CAI easily and return your tune to stock easily too.

 

I boughtan extended warrenty on my car and my transmission crapped out on me and had a power window motor give out and my ac compressor go and I have near full bolt ons and didn't have a probblem getting the stuff fixed.Obviously it's not always that easy though..