There's absolutely nothing wrong with a 4-bevel gear differential. Check out
http://auto.howstuffworks.com/differential2.htm for an animation of what it would look like.
As for reducing friction, I don't think it will do that. What it will do, however, is distribute the force more evenly over the two gears, thus reducing the chance of tearing teeth off, etc. Then again, I don't really know all that much about differentials so I could very well be wrong on that last point.
--Rob