Pretty much all the scuffs on my bike is from the ground running into it, as for your question, you can use fine grit sandpaper like you said, it's going to dull the finish though, you can try this liquid polish also made by Mothers. It works best on plastic headlamp lenses, but ok on bike plastic, this will help bring back some of the finish. Or you can just slap on some decals and number plate backgrounds to hide it. Or be like me and just show all your battle wounds……for character.