I was just thinking about that. In the car detaining world you can buy a glass polish for removing microscratches from windscreens, perhaps polishing with a Dremel polishing pad.
Solvol Autosol metal polish works really well on many different surfaces, including acrylic watch crystals. Automotive paint scratch reducing polish would work well too Toothpaste takes forever as its not abrasive enough. Polywatch is designed for the job, but you can use other micro-abrasive polishes with just as good results.
Dremel not a good idea and not really necessary - the speed makes them skitter about and they would generate a lot of heat quickly.
A piece of rough cloth or paper + your chosen polish is what you need - fold it into a little pad and just apply "a little" pressure and polish in easy circles, The combination of micro abrasion and the heat generated will reduce the scratches in a few minutes and you really can often end up with a flawless, sparkling crystal good as new. Newspaper or brown paper work well for the initial scratch reduction, then toilet paper or a soft cloth to finish.
This only works on acrylic plastic watch crystals btw - it they are made of glass then forget polishing scratches out and just replace then.
Acrylic has a warm, slightly yellow tint and should be warm to the touch
Glass has a colder tint and will be cool / cold to the touch
