I got my bumpers painted a year back and got the same feedback from some body shops, but at the same time there were many body shops that were ready to do it.

I was told that the textured bumpers were not a good choice for painting and would require lot of surface prep for the paint to hold. Finally I got it done at a body shop that does Ferraris and Bentleys. I also put paint protection film on it to prevent any damages from road debris. The results were amazing and I have had no problems so far.