Much as I'd like them to fix Gollum in Fellowship (IIRC the design wasn't finalised so the version we see looks nothing like the Gollum we see in the subsequent films), and there unboubtedly is a bit of dodgy compositing going on in all three films that could also be touched up, it's a slippery slope and we don't want to end up with another Star Wars situation.
Do we see anything more than his eyes and fingers? I never noticed a discrepancy between
Fellowship and the later two.
I'm very happy with my special edition boxed set and have no intention of shelling out for a new version with different actors green-screened in. If it ever happens, which I think is unlikely. Peter Jackson has always struck me as a man of integrity, unlike that cash-grabbing tool Lucas.