By all means, keep the human player.
As for the big finale, definitely put something in the middle that robots take aim for. A bar, a ramp, heck, let's have a cargo net this year.
On the subject of cargo nets, I'd be thrilled to see a game that required mobility other than a drivetrain. Monkey bars, for example--they'd require skill to navigate, and you might not be able to get that fifteen-motor drivetrain built, meaning rookies wouldn't necessarily be bringing a knife to the gunfight with a kitbot.
Similarly, I wouldn't mind seeing a field with varying terrain. Perhaps in the manual, FIRST defines four or five six-foot squares, each with a certain feature, like a small stack of two-by-fours. There'd be N of each square on the field, placed in a different-but-mirrored setup at each competition, with a uniform setup at the Championship to make the Einstein matches sane. Think vision tetras, but they stay that way for all three days.
Finally, one that might be a mixture of a game element and technology--score the game in real-time. It'd be harder to execute, granted, but I believe FIRST's ability to do so has improved dramatically over the last game scored that way,
1995's Ramp n' Roll. With some Banner sensors like in 2004 (where catching the reflective tape in the ball tees triggered the ball dumps), I think goals would be doable. And teams could always emulate the goal without the electronics.
Just my thoughts--whatever comes out, I'll play it.