I love wagon lists, they can be pretty amusing and allways tend to dent anything they come up against
a few ideas though:
Throw in a standard warboss, this way the mega nobz can be scoring units aswell.
Free up some points and either add kannons (S8 is nice) to the wagons, or add zzap guns (not too reliable, but a nice chance of a S10 shot)
failing that (cheap option) add boarding planks to all your wagons (5 points each)
that way the nobz in each unit can make thier full number of attacks on a vehicle within 2" of thier wagon.
meaning they never have to leave and also add some anti-tank to the army.