Anytime you're painting a smooth surface like that, glass, plastic, metal, hit it with red scotch brite pad to scuff it up a little otherwise the paint won't stick and will eventually peel/flake off. Also wipe it clean with rubbing alcohol to clean any grease as paint doesn't like to stick to grease/oil/water. Krylon is usually pretty durable and sticks to damn near anything, though.
What did you use to wipe off the emblem marks after you took off the word Pontiac and what was the exact spray paint you used I want to do this for my g6