Little late on this, but figured I'd put my thoughts in anyways.
Wembley is a really hard character to truly replicate/recreate, in my opinion... Steve really found a fine line between (in terms of voice, anyway) overly raspy/squeaky, and and almost a childlike sense of whimsy and indecisiveness, which lent itself to a higher voice. To try and redraw that line between the two with another performer, regardless of how talented, will create a hard challenge.
As someone who's attempted (and failed, for the most part) to perform Wembley on seeral ocassions (videos are still on MC in the Fraggle forum, if anyone's interested; they're outdated, but meh), I can verify (at least for me) how difficult finding that line can be. Just a fans perspective on his favorite Henson created character, I suppose.
I've heard Clash performed him in late 2016, actually, so take that as you will (during a celebration for Dave Goelz).