Well done on developing the Roboduino,
Just reading through this thread. Did you throw away the idea of a robot arduino shield? That I would buy. 50 dollars extra (when I already have an arduino) for convenient headers isn't worth it for me (while I'm sure it would be for others).
With the amount of Arduinos sold already (approx 20,000), I think you would have a nice market for selling shields. I think people would be much more inclined to pay 10 dollars for a robot protoshied, which is only a pcb with some headers. Sell it as a kit and it should be very cheap to make.
Anyway it just a suggestion,
Well done again