The strangest live version of "Wouldn't It Be Nice" that I've heard is from an Arizona show in 1988. It's actually kind of a mess, as it sounds like nobody can decide who is supposed to be singing the lead. At various points, Carl, Al, Mike, and Jeff Foskett all kind of trip over each other singing the lead parts, sometimes in unison, sometimes unintentionally so. Even Mike starts doubling (or tripling) the lead prior to his bridge.
Can't remember, I have to look.
I vote Al even tho he forgets the words sometimes.

Carl too.
http://www.youtube.com/watch?v=72d4En8BJegI don't like it when Mike sings lead on "Help Me, Rhonda" at Knebworth or WIBN in Melbourne with Al.