I suppose the only option is to gear down those kinds of motors. But solar power doesn't provide much total current per blast, so it may not be enough to move an entire tooth before it stalls. I'd like to design a solar engine that would pump-up small voltages, perhaps from a group of smaller capacitors and into a large storage capacitor. To reduce weight and size, soldering together surface-mounted components might produce a really peppy B.E.A.M. robot. Even with touch sensors and greater spunk, I'm not sure the behavior will ever be as exciting as a microcontroller-based robot.
BEAM robots are fast and easy to create.
They're a good way for newcomers to get started in robotics.