Scratch-Off kits, about $37, have four different grades of polish and a couple of drill operated foam applicators.
I just two days ago did my windscreen after 1600 hours of cleaning bugs guts from it, as well as miscellaneous scratches and general cob-webbing. I should not have waited this long - the results were dramatic. I used one of these kits 17 years ago during the construction to remove a few deeper scratches, but the compounds had all dried out, so I bought a new one. Since I could not feel any of the newer scratches, I only needed to use the finer two compounds. I did have some very noticeable scratches, which I believe came from some contaminated cleaning cloths I was using.
I also had a number of scuffs, etc., on the inside of the slider's windscreen. Since I couldn't use the drill there, I simply used elbow grease. It didn't take very long to clean that up. I think less than 2 hours total time was needed.