I've done "Rainbow" in many styles, and I never remember it failing to satisfy the crowd. A good song can do that. Personally, I love doing it on uke in Izzy's style, but I often do it with straight two-handed Rhodes piano. No one remembers the disco version by MECO, huh? They did medleys of Wizard of Oz, and Star Wars ... fun break from the regular din on the dance floor.
I could listen to Eva Cassidy all day. Such a talent.