For sure, the regen braking doesn't do a whole lot to add to runtime. I think the main reason is to provide a place for the energy to go, the added runtime just happens to be a collateral benefit.
Way ahead of you lutach:
http://www.rc-monster.com/forum/showthread.php?t=4997
It appears I didn't post it, but I do remember making a three-phase bridge rectifier and capacitor filter and it did provide a decent amount of power (don't have the numbers though).