Here's what my K75S windshield looks like after spending about 6 hours going from 400 through about 6 steps up to 2400, polishing with Perfect-it and Novus, and clear coating.
Sometimes the crazing goes all the way through the plastic, not just on the surface. When that happens, there isn't much you can do to make it look new. To be honest, compared to what it looked like before I worked on it, it really looks very good. This windshield had been parked out in the Florida sun for something like 20 years. My guess is that besides the UV damage, a previous owner used window cleaner with ammonia on it as well. For $10 I couldn't complain, though.