What about having multiple game pieces?
I don't think this has ever been done before (someone correct me if I'm wrong).
I don't have any ideas about what those pieces should be other than that they should be very dissimilar in order to force teams to build different mechanisms to handle them. (I.E. poof balls and pool noodles)
Also, I think that dynamic alliances would be an interesting thing to see. You wouldn't be able to use bicycle flags to ID the teams, and the LED flashers probably wouldn't work too well either (rotating bubble lights maybe?).
Anyway, after some amount of time, the alliances are randomly selected from the robots on the field. The alliances would remain the same size, but they'd be made up of different robots.
(I.E. In period 1, the blue alliance is made up of bots 1,2,3. The red alliance is made up of bots 4,5,6.
In period 2 the blue alliance is made up of bots 3,5,6 and the red alliance is made up of bots 1,2,4.)
Maybe even have 3 alliances (red, blue, green) and see what happens. Heck, you could even start the match with 2 alliances and the green one wouldn't even exist untill half way through the match. Crazy!
The field should also be covered in sand. (Wasn't the first, FIRST competition held on a field covered in popcorn kernels?)