Great fun to read and really interesting ideas. You sure seem to know this game well.
Sadly I have little to contribute myself but I've noticed two oddities when playing against some friends.
THE LEFT HAND OF AN EMPEROR HOLDS THE DAGGER UNSEEN
Most people seem to become blinded by the idea of fielding enormous armies. Rows upon rows of warriors in shining armour. Their swords held high in honor of their lord, gleaming in the sun like a bountiful harvest of steel. The strength of an empire made physical form. Impressive yes?
It would be well worth keeping that nice sight intact would it not? Mountains of gold spent. Years of preparation. So why risk it when you do not have to?
Cut of the head and the body dies, as the saying goes. Ten assassins can do more harm than army one thousand strong. Fifty assassins can change the course of the war entirely. One hundred assassins and your enemies will throw themselves at your feet, begging for mercy from your unseen might.
Creating an assassin "guild" in a province that is out of the way and mostly worthless is always a good investment. Add a mage with no other buisness then the steady construction of cheap but dangerous tools like Dragon Helms, Skull Talismans or Snake Rings. Assassins are cheap when compared to most commanders and expendable. It's a lot of micromanagement at times but five Groups of ten assassins can create an endless migraine for your opponent and tie up a lot of resources that would otherwise be used against you.
SUMMONED UNITS DON'T HAVE UNIONS
What's better than a loyal soldier ready to give up his life for your empire? One that doesn't ask for a salary. Summoned units, save Trolls who are all members the Bridge Squatters Union, don't have a gold upkeep. The Monthly Ritual command is not to be ignored. Having a mobile provincial defence is quite worth it's cost in gems. And some summons even summon their own units! Remember that the next time you think about purchasing that new regiment of shiny knights.