Not very much. I had an LG that was scratched during a botched repair from the repairman. The jackass offered to buy it from me for about $20 (to salvage the parts) but he was the one that screwed up the repair. At least he "agreed" not to charge me for the service call. Bleh... The problem is similar to CRTs, the front had a matte coating to prevent glare and most fixes also "polished" the matte. It seems most solutions assume a glossy screen.
I really only experimented a bit before tossing it into the parts box. I decided it was a put up or shut up kind of thing.