I will take some exception to the OP's unqualified description of muppet guest stars as "B-list".
Just off the top of my head, Peter Sellers, Debbie Harry, and Elton John were NOT B-list when they appeared on the Muppet Show. I suppose Sellers might be considered more of a specialized taste, but that's not the same thing as saying he was past his prime, ready for a guest-spot on Fantasy Island. The Pink Panther films were huge, and Being There certainly solidified his art-house cred.
I'd also mention Alice Cooper, though I do seem to recall that by the mid-80s, he was regarded as a has-been. Not sure what his status was at the time of his Muppet Show appearance.