I like this. I was thinking just about the same thing, so let me add my version of this:
I feel that Essence should not be a character stat, but rather given in small amounts by the land area you command, and in greater amounts by special locations you command (such as Shrines on Earth, Air, Fire, etc. nodes).
Essence should be used up like the food resource, and should be available to be spend on fun things such as:
1.) Land Fertilization/Beautification (Land under the DIRECT influence of your cities, i.e. very very close to them) should
COST essence, rather than provide it - as the Channeller is actively making the land more fruitful).
2.) Upkeep cost for strong magical troops (smaller troops might be paid each turn in mana, bigger troops should use up a certain amount of essence).
3.) Enchanted Weapons and Armor.
The most important issue would be that essence is refunded into the global pool once it is not used anymore. So, if my essence pool is 20 due to the amount of land and shrines under my command I could use up:
1 point for my small city, 2 for my medium city, 3 for a large one - leaving 14 in my pool.
Of these 14 I could use up:
4 for 4 large magical troops, 4 for magical weapons and armor for my champions - leaving me 6.
Now, when one of my large magical troops dies I should have the essence refunded - bringing me back up to 7 - the same principle should apply for losing cities, or destroying enchanted weapons and armor.