Depends how bad the dings are. If they're small, just try a touchup with a black Sharpie pen and don't look too hard. Once you start with paint, you run into blobs and it becomes more obvious. There are touchup kits for cars available with blob removers, but, not knowing what your box sets are made of, I couldn't say whether it might be damaged by the chemicals. May be best to just put them in some nice plastic sleeves and prevent additional damage.
