I had the headers on my Bonneville ceramic coated a couple of years ago. As has been stated it does scratch a bit and mine developed a kind of brown undertone (original color is black) after being run in rainy weather. Not sure what happened but they still look good.
PS Bonneville does not have the heat shield like the America so the part you see endures more heat than the America would.
Bottom line is I would do it again... the bonnie pipes were blued as far as the bend toward the back of the bike before coating.
