A capable player in ANY CLASS is a very valuable add to a group. Anyone who says otherwise doesn't know what they're talking about.
I agree. A good player, in any class is an immense help to the group. I once ran VC with a rogue, he was twinked, but regardless, he tanked for quite a while until we could find a tank and healer.
A good player in any class can not only do his job well, but help other players with pointers, if they're newer.