You can buy several different types of lexan plastic at most hardware stores. It looks like you might be able to change them out completely. Working with this is pretty simple, basically score it with a utility knife and break it on the seam (similar to working with tile, but usually easier).
Aside from that, you might have some luck with something like a car headlight restoration kit or similar. Basically something which is designed to remove the contaminants off of plastic and get rid of the haze that can tend to build up on it over time.