Just reloaded act II to re-run it and get some more research before running into act III and after finishing something with Henry's daughter one of his skills increased by...1. Still though, at the cost vs reward of using them I doubt I will be trusting many battles to any of them.
I like them and the stories they offer and would love to have some kind of leveling system for them (side quests!!!) but at the moment they have little to no value on the field.
Wouldn't it be cool if the generals ask for the dragons help every now and again? A quick little battle where the units are all AI controlled and you just fly in to offer a little aid? Oh well, add it to the wish-list.