My windscreen is 8 years old and has lots of tiny (micro) chips and abrasions. Is there anything you can do to polish these out or improve the smoothness of the glass again?
Autoglass told me at the time that those chips large enough to be repaired will be filled with special resin, anything else they will just leave alone.
I think that if the windscreen is in poor condition you will need a new one, unless someone else knows better...