I believe that it is Dionne Warwick as well, however... Is that too easy? Her voice is so distinct, I don't know how it wouldn't be recognizable. Having Dionne on is like a freebee to viewers.
It's the only reason I like the Maya Rudolph theory. I think it wouldn't be that much of a coincidence having Maya and Martin Short competing in the same season. I think Martin may be the taco. Bob Saget is kind of tall, isn't he? it's good guess, but the taco didn't seem particularly tall. The way Taco talked during the clue package, made me think he is Martin Short.
I'm not going to disagree with any Bret Michaels fans. I thought Bret was heavier than the banana appears, but I haven't seen him in a while either. The clues did seem to point to the Rock of Love series.