I just had this done on my gli. I used Stinger RoadKill, got it done from the same shop. Aamir charged me 7.5k for both front doors (multiple sheets went in), and I'm very happy with the difference it has made. It wasn't as expensive as I'd imagined, and the rattle is completely gone (my sub used to make the front doors rattle something fierce before, and now the rattle is completely gone). If you knock on the front and rear doors from the outside, the difference is clear. Also, the front doors now close with a nice solid "thud", compared to the noise they used to make.
I might go back to get the boot area done, although for now I actually don't hear the need to. Its also a good thing to have done on your car, if you're even semi-serious about car audio, because with the much lower road noise, every sound out of the front components is now more detailed and, well, rich.