Vinister, you're right about the standard use of the foam. I will say that not all foams are created equal. There are far lighter foams like 2 and 5 lb which offer no real structure beyond the shape that they hold. I usually use 15 and 20lb foams which get to be like working a piece of balsa.
Regarding it's use, I agree that it should not be used as a load bearing part. A trim bezel however is rather far from it. I've made other variations of the bezel including one that incorporates a few plies of carbon fiber on the lower portion which makes the whole piece (unreinforced otherwise) more rigid than the ABS part that came on the car... but there is no bondo on the part. it's just foam/primer/bc/cc. I am experimenting further with creating a silicone rubber mold based on this and using polyurethane resins to create multiple parts... so to say, using the foam for that which it was intended.
i did do the paint myself. I went and had a lady at the paint store match my two interior tones for me. Provided you take care not to contaminate your paints with anything, it's actually quite easy to get that finish. No wetsanding or buffing was needed there.