One thing that I think is missing in Elemental is good old espionage and backstabbing. For example games like Total War, Masters of Orion and Koei's Romance of the three kingdsoms all had kickbutt espionage options that gave you an alternative route to winning.
So my suggestion would be to take the best aspects of espionage from these games and add it to elemental so that you can achieve victory another way than just magic or military might.
First allow the creation of spy units or allow leaders to train in the path of the spy that would give them the option to perform espionage feats.
Here are some examples:
1. Allow spy units to hide themselves and give them the ability to move through enemy terrain without being detected, unless scouts are being used to search for spies or the sovereign casts a reveal terrain spell.
2. Spies are able to infiltrate enemy cities, once they are in an enemy city they are able to perform.
- Incite Unrest - Spies are able to raise the unrest of a target city. Cities with high unrest have a chance to rebel against thier sovereign and become an independent city.
- Embezzle Funds - Siphons a percentage of the cities income.
- Steal information - The spy steals a portion of the cities research and forwards it to the owner.
- Sabotage - The spy attempts to destroy a city improvement.
3. Other activities that spys can perform:
- False Flag - A spy attacks an enemy unit, while wearing another factions uniform with the intent of causing a war between the two factions.
- Betrayal - The spy attempts to persuade an enemy unit to switch sides during an attack.
- Assassinate - The spy attempts to assassinate an enemy leader or champion. If the attack succeeds the leader or champion is out of action for a number of turns and suffers an injury.