I'd be less worried about the crowds being bored for one fight than potentially putting off new blood, because they can't enter a simple first robot with the big boys. Part of the attraction for us was that we could make a robot powered by drill batteries and made out of any old anything, and still have a chance to beat a champ. Taking that away may further slow the flow of newcomers.

Perhaps a compromise? A rambot that does under 10mph can't weigh any more than 8 or 10kg?