I find it hard to imagine the show without the original cast. They were just so perfect. It was one of my first broadway experiences. I saw The Light in the Piazza, Spelling Bee, and Spamalot. I still have no clue how Spamalot won over two of the greatest pieces of modern musical theatre.
It's interesting, I've seen it done with actors giving performances very close to what the original cast did and with actors putting their own spin on the characters. Both worked because the material is so strong, but that original cast was just perfect and no Olive has moved me quite as much as Celia Keenan-Bolger. I agree that Spamalot winning is a real WTF in retrospect. Featured Actress was also a crazy category with Celia, Kelli, and Sara.