With regard to the hidden immunity idol, I like the concept, but I'm not sure how much it really impacted the game since Terry kept winning immunity and never let anyone else use it. Guess it did keep him in the game for the last vote since everyone either knew or thought he had it and he didn't receive any votes.
Actually, for quite some time I had hoped that Mark Burnett would mix up the game with some challenges or things that would allow other players to have more impact on the game. I was thinking along the lines of the game "Uno" where you can use cards to mix things up.
Obviously, you wouldn't actually use "Uno", but allowing contestants to play items against one another, such as some item that allows a player to replace another on a reward challenge, get extra food only for themselves, or give them a slight advantage in a reward or immunity challenge (say a one obstacle head start, etc.). Something that allows the game to be a little more cut throat so that players and viewers get a better sense of the contestant's character, etc.