dunno about it being a gimmick if it was all traxxas RC's would have them, and a sticker that says NOW WITH SPIRAL CUT GEARS to make it sound cool.

But from what I read they can handle more power due to the larger contact area, but put more load on the bearings so kinda seems meh as benefits

Here's one example of the pinion bearing being screwed over (and by an outrunner which is your favorite type )
http://www.rc-monster.com/forum/show...77&postcount=8
if you look at the main thread there's even pics of the spiral diff carnage on bearings