I've done that twice now. The first time, I got the bumper repainted for free at the dealer because of some recall or something about the bumpers being attached too tightly and chipping the paint where the bumper and the top of the fenders meet.
But alas, that didn't last very long. So far, I haven't done anything about it and no one notices, but it bugs the hell out of me just knowing it's there.
The cheapest way would be some touch up paint, cause odds are you're gonna be the only one that notices it. Repainting the bumper could cost ya a couple hundred. Finally getting a splitter really boils down to if you like the way it looks.
Hope you find the best path, and that I might have helped.
