Actually what you described for unloading is a little in reverse.
With the current MT setup of a tranny center you have no unloading of power front to back - front and back wheels are always getting the same power with a locked center driveline.
With a center diff - if the front wheels come off the ground then the motor power will push to the unloaded front wheels and you'll get less power to the rear wheels - the thicker the diff fluid you put in the center diff will reduce the unloading of power to the front wheels and give the rear wheels more power.
I've read in other threads that the Traxxas center diff is pretty weak, only has two gears in it so you have to use much thicker oil than you normally would, can't stand up to real BL power, and really isn't worth the money.
Personally I like the locked center in the MT - just makes it more fun for bashing around and wheelie action.
