Its a never ending cycle. I learned from my 335i to stop being anal about every scratch and dent and rock chips. After a few years of it, I just got tired out from worrying to keep my car in perfect shape. Only was that was possible was to not drive it, but then there is no point of owning it.
If it bothers you, respray it. Knowing that something else will eventually happen and this process will repeat. As much as you can try to prevent it, Murphy's Law always win. Bumpers are meant to be scratch up.
I would leave it in there since its on the bumper. If people ask, say you got those scratches when you saw a shopping cart about to run over a toddler and you moved your car to block the way and saved that kid's life.