Bumpers "To paint or not to paint" this is the question ?

Personally....I prefer chrome. Mine is painted black only because when I bought the car they were that way. I have gotten used to them being painted but as soon as I can they will be re-chromed. Personal preference I guess, and for your question they can be sanded with anything from 180 to 80 grit according to the shape they are in. Definitely a urathane self etching primer must be used. I have had to repaint mine because they were not done correctly, they were done in flat black and I changed them to satin black.