DO NOT REPAIR ANYTHING, it only hurts the value. I leave all my signs in their original cool vintage look.
If it absolutely bothers you, just use paint (on porcelain signs only), so it can be easily removed by the next owner.
There are a couple auction houses in my area that are removing touch-ups prior to the auction, so the buyers can see the true sign. I think that is a stand-up way to do business in my opinion.