My idea is to have a debate bracket. Two candidates face off at a time, and the winner (determined by combination of random surveys on-site and telephone (if televised)) advances to the next level. Yeah, someone could get shafted, but these are the early days. At least this way, a lesser-known candidate could get some exposure if he debates especially well.
Would you have 10-hour debates—or 50 debates?
I love the debate bracket. Let the two debate according to rules and very little input from the moderator. The bracket can even be held in the same debate. Take three or four hours, with breaks, and when there are 4-6 candidates, have each winner debate each other, and finish the whole bracket in 4 hrs.