I happened to be involved with the 29" wheel from the beginning. 700c wheels have been around since the late 1800's but until Mark Slate at Wilderness Trail Bikes (WTB) made the 52/47 (2.1) Nanoraptor in the spring of 1999 10 years ago the 29" designation which is the overall diameter of the wheel with a Nano mounted, did not exist. This is the first bike that ever had the tires mounted on it in the spring of 99' in CB, CO.

The biggest benefit is as mentioned, the ability to roll through and over stuff with just that much more ability than 26" which has that much more ability than 24" etc. and it does so at lower psi due to the higher volume of air in the tire. The highest pressure that I have run in the last 10 years is 30. I have had fewer flats in that time than you can count on one hand whereas before I had a flat more often than not running 40+ in 26" wheels.
The argument that there are not enough parts available and that the wheels are weaker is bunk. Even in 99' we had suspension front and rear as evidenced here, my first 29"er,

I have a wheelset that has probably more than 3k on it using rim brakes and I have had to true the rear maybe once a little bit after original tensioning and it has seen mostly singletrack in the Rocky Mtns. type of use. YMMV of course, but I doubt it.
What can 29" wheels do for the MB world? I am not a big proponent of the use of MB's offroad, but roads themselves can be pretty darn rough if you factor in all the chuck holes, speed bumps, cracks, dirt etc.. What we find using a bike like this

is that it reacts much better to these obstructions at speed than a 26" wheel can. We are going to continue going down this path and as time goes on we will have more data to support this.
One of the arguments about the larger wheel size is that it does not suit smaller riders. In the pedal bike world I would maybe agree with riders 5' or less. I have ridden with 5' 1" women riders that just plain rip on theirs. But the extra rotational weight makes it a bit harder for them to spool up, but once they do they roll more efficiently. With a motor this melts away and there is no reason to not use 29" wheels for MB's and MAB's other than the fact that they are not socially acceptable in this genre any more so than they were accepted in the Mtn. Bike world back in 99'. Things are slow to change in the bike industry, but the early adopters get the biggest benefit from being receptive to new ideas. As long as the idea is sound anyway.
Next on the list is 36" wheels!
Or big fat wheels?
In the meantime ride what you have and be careful out there!