The things that make up a game's overall appearance are the marquee, side art, control panel, monitor glass, instruction stickers and other misc. Most of the games people tend to collect are as much as 20 or more years old and have spent the good part of their lives in an arcade being hammered by young brutes bent on beating the machine into submission. It usually shows. Control panels get cracks, tears, burns and spills.
Marquees get cracked, start flaking and fade.
Side art gets gouged, scratched, removed, scuffed and even painted over. Monitor glasses get broken, scratched by vandels and fade. You know the story all too well. Finding replacement art for your game can be an expensive if not impossible proposition. The companies that originally made these games are either out of business, or not interested in making new art available due to the lack of profit potential.