Here's my
1. Can't compare before and after of the GMPP tune, since I got mine done by the dealer in the original sale, but I can certainly say it's fun. Others will say you can get more power from other aftermarket tunes (Westers or Trifecta to name just two), but I like the GM warranty coverage part of the GMPP one, myself.
2. Definitely need to get the clear bra from somewhere. My car already had chips on the paint when I got it home (about 80 miles on it!). Kappasphere is DIY and expensive. Getting it done by someone is even more expensive! Here are the alternatives that I did:
a. Got the 'factory' GMPP rocker-panel clear-bra pieces from GMPartsDirect (about $82 incl shipping, part# 19170307). This is DIY, but is not so hard to do if you are friendly with a heat gun. Dealer price is about $95 if memory serves. Make sure you have all supplies first (spray bottle with water w/2 drops baby shampoo, flexible plastic squeegee, towels, dust free and warm area AND the heat gun!)
b. I got a bumper and hood clear-bra kit off eBay for $37(!) CAVEAT: cheap kit, so you may only get what you pay for. It was difficult to apply because it wasn't as stretchy as the Ventureshield/3M stuff is supposed to be, but went on well enough in the end with a lot of application of my heat gun (though it took me maybe 4-5 hours!). This will at least last me through the winter.
I recommend that you first search Youtube for videos of "how to's" for clear bra!!! Let's you know how to prepare and what you're in for.
Hope that was useful. Good luck.