That sucks, I feel your pain I've had all sorts of damage occur from taking machines to shows in the past. Some people are just a**holes.

Unfortunately I don't think you're going to find a fix for that (other than replacing the glass) and the tricks that you read on the internet are more likely to make it worse IMO. I've tried many things in the past to repair scratches on CRT monitor tubes after people smashed through the protective glass in front of em like on Golden Tees and other arcade games. I've tried the toothpaste thing, wax, all kinds of products including cerium oxide. The latter had the best chance of a slight improvement but I literally spent hours polishing and got so mad at the lack of improvement that I polished the monitor tube with a drill until it overheated and burned a hole into the tube and imploded. Felt so good...til I had to dispose of the monitor

As much as it bothers you though, it's not likely to detract from the value of the game much (if at all) when selling it so I wouldn't let it get to you too much.