Hey All,
On an electric, it might not make much of a difference, because most of the sound comes through the pick ups anyway. However on an acoustic, anywhere that you put your hand on the guitar, even the headstock carries vibration. Much of the sound does come from the sound hole, but not all of it. I've never tried putting stickers on a guitar, but I would think that putting them on the top, would really cut down on the vibration through the body.

I used to put stickers from the places we played on my cases, always thought that looked cool. I can say this, after them being on there for a few years, I'm glad I didn't put them on the guitar. When I tried to clean the case off, the stickers came off in pieces, and I never did get all of the adhesive off of it.

The choice is really yours, but I would advise you not to put stickers on your guitar. Another thing to remember is the guy with all the stickers on his guitar, more than likely has an endorsement. He gets new guitars on a regular basis, where you may have only one.