I think it's totally feasible to keep brushed DC motors idling to reduce spin-up with a simple motor controller, but I assume it would put a lot of wear on them.
It would, and absolutely kill your battery life and increase the complexity of the wiring setup, compared to a direct-to-battery brushed motor setup.
Remzak is correct about brushless motors being very efficient, probably by at least a factor of 5 (I think I remember hearing that brushed motors were about 5-15% efficient while brushless were 75-90%), depending on the setup. And except for the bearings they're practically immortal, as long as you use them as designed.