I dosed mescaline and LSD together and loved it. I don't really see how the combination is anymore "redundant" than any other psychedelic combo. The two provide very different headspaces; mescaline is gentle and loving, LSD is lucid, analytical, and all around crazy. They combine well; the mescaline "pads" LSD's headspace without making it lose any of its edge. Not to mention, I personally like mescaline's melty/flattening visuals better than LSD's, so the combo really adds to the visual aspect.
Oh, and another big thing that mescaline has to gain from LSD is music enhancement. Not that mescaline doesn't enhance music, but LSD is just tops in that arena.