In Fla to use old plates, they must be sent back to Tallahassee? for approval first. At some point, Fla started using reflective type paint, not sure when. I do know when on my old permanent semi trailer plates and they started to look weathered, they wanted them replaced with a new replacement. I suspect it might be difficult to have a plate "restored" with the proper reflectivity, etc a desk clerk in Tallahassee will approve, and you will be left with just a high priced collector item. You get approval first? and then get it restored, not sure an LEO would care enough to spot or cite on a restored car if the plate looked nice