I've destroyed a number of old cds and dvds to see how they were made. For cds, they're basically a piece of plastic with a very thin reflective layer on the very top. Very easy to damage on the top where all the data is. DVDs, seem to be better. The top usually has an extra coat of plastic over the reflective layer.
Anyway, to make a short story long, I've repaired a number of scratched cds by polishing them with a dremel tool with a cloth polishing wheel. ONLY the cloth wheel works. DO NOT stay in one spot, keep it moving. Use lowest speed. For deep scratches that aren't easily fixed with the dremel alone, toothpaste or very fine sandpaper (1500) followed by the dremel works for me.
The commercial kits essentially do the same thing. An abrasive and a polish. I think that they do a better job but they cost a lot more also. Last time I saw a machine, it was @$100CDN and the refills for abrasive and polishing wheels were fairly expensive.
Best option is to not scratch them in the first place.
Good luck.
