As for your take on Josh, I totally agree. He was on! And I was thrilled to see his "Nick"-style playing of the tenor guitar - right hand furiously strumming. Even his voice had a twinge of Nick's quality and style. He was having fun and really stole the show in my opinion.
Also at the top of the "on" category for me was Andy Corwin. I've been a fan of his ever since I saw him impersonate Lou Gottlieb on "Have Some Madeira."