Given their popularity, I'm sure they've been allowed back in. :-)
The Magic Circle still asks them to donate items to their museum, despite refusing their membership.
The Magic Circle is quite different. It's not generally open to the public and is, frankly, quite old fashioned. It was only very recently that they even started permitting female members. For that reason alone I doubt that either Penn or Teller would ever want to go there. They'd probably be more likely to actively protest against the Magic Circle (at least until recently).
It would make more sense if perhaps P&T were "uninvited" from the UK's Magic Circle, which is a very different, much smaller and entirely unrelated private magic club. The Magic Circle only very recently started allowing female members, so I'm pretty sure P&T would be delighted to be banned there.
Otherwise, I don't think the issue is spoiling it for audiences as the craft and presentation style count as much or more than the trick itself.