Good stuff Kevin.
As Andy mentioned, I use 'T-Cut' for polishing scratches, particularly canopies. This is a brand name for a 'cutting compound', in liquid form, similar to, but not the same as liquid metal polish, used for colour restoration on car body paint work - a similar 'polish' will be available in the USA.
Although toothpaste works very well, the 'T-Cut' is better, and can 'restore' even the deepest, worst scratches and 'frosting'.
One thing to note though - apply it and polish off as soon as possible, as if it's left on the clear plastic surface too long, it
might make the plastic brittle.
The pics below show a 1/32nd scale Beaufighter canopy, after removing heavy frames, applying the 'T-Cut', and after polishing.