I think it would be really beneficial if city enchants did NOT scale with the essence in target city, so a city enchant in a 1 essence city is worth the same as a city enchant in a 3 essence city.
This will also help make grain and materials a noteworthy resource once again, instead of everything being about essence
I don't mind essence being important, but essence being so awesome that grain and material takes a step back and become next to worthless is really sad.
Another idea by Madcatter is to let city enchants scale per level, I will put initial thoughts up on this (plus clean up a little, to remove ideas when two different ideas represent the same concept.)
I will come with suggestions for what the spells should do when they are not scaling with essence:
Unit Boosters:
"Aura of Grace: When enchanted city trains a unit, the trained unit gains +2 initiative"
- Would be awesome if it was given a +2 initiative trait also, so we can see what units was trained with this buff more easily.
- Trained units gain +1 initiative per city level.
"Aura of Vitality: When enchanted city trains a unit, the trained unit gains a +4 HP"
- Would also be awesome if this was given as a +4 HP trait, so we can see what units was trained with this buff.
- Trained units start with 1 more HP, +1 per city level. (level 1 city boosts with 2 hp, level 2 city boosts with 3 hp)
Economy Boosters:
"Avarice: Enchanted city produces +3 gildar per season due to the drive to make money"
- or percentage bonus "Avarice: Enchanted city produces +20% more gildar each season due to the drive to make money"
- Enchated city produces +1 gildar per season for each city level.
"Enchanted Hammers: Enchanted city gains +1 Material"
- Alternate version could give +10 production.
- "Enchanted city gains +10 production due to the population working tirelessly"
- Enchanted city gains +4 production for each city level.
"Inspiration: Enchanted city produces +2 research per season"
- or a percentage bonus "Inspiration: Enchanted city produces +20% more research each season due to a rush of inspiration affecting the scholars"
- Enchanted city produces +1 research per season, per city level.
"Meditation: Enchanted city produces +3 mana per season"
- or a percentage bonus "Meditation: Enchanted city produces +25% more mana each season due to the native channeler's in the city focusing the magical energies into raw mana"
- Enchanted city produces +1 mana per season for each city level.
"Nature's Bounty: Enchanted city gains +1 Grain"
- Nature's Bounty: Enchanted city gains +60 food, due to the magical energies affecting and reinforcing crop growth
- Enchanted city produces +30 food for each city level.
- Enchanted city produces +1 grain for each level.
"Gentle Rain: Enchanted city produces +25% more food due to the magical energies controlling the weather, to create the perfect farming environment"
- Enchanted city produces +20% more food for each city level.
"Pit of Madness: Enchanted city produces +3 research per season, but suffers a -1 growth per season, and units attacking enchanted city will be struck with fear"
- Enchanted city produces a +1 research per season for each city level, but suffers a -1 growth per season, and units attacking the city will be struck with fear.
"Sovereigns Call: Enchanted city receives +1 growth"
- alternate: Enchanted city receives +2 growth, but a 10% penalty to production due to resources needed to build new houses.
- Enchanted city gains +1 growth for each city level
- Another thing you could do is to make this percentage based, to keep prestige being an important attribute, instead of being made useless by a spell taking its job.
- Enchanted city gets a +50% bonus to growth.
- Enchanted city gets a +20% bonus to growth for each city level.
Other:
"Blood Sigil: When enchanted city is attacked, all defending units will be under the influence of Berserk (Lose 1 hp per turn, but gain +3 attack), and attacking units will be under the influence of Wither (-3 attack)"
- No real change to this, re-described it to my own liking 
I don't have access to the other spells right now, so please type them up below with description and I can give a suggestion to the balance.
I can also work for some more interesting descriptions if there is a need for this 
Hope you guys agree though
Sincerely
~ Kongdej