Here are some.
So, I though 'bout some small things, which will mix up experience of gameplay just a little bit, but won't be any big importance anyway. They would be there to simply give player 'little bit of concern, all only if he is willing to concern. Such would be:
1. Gods blessing.
Idea is, that in each map, when everything starts, bu simple or smart algorithm, one of many god blessings come into. They bless all living souls, giving to them very small bonus.
Those could be any kind. Example - blessing of some kind of Elven goddess (Sehanine, say, like in D&D), which gives to all ranged attacks +5% power. Or Some ork God, (Grumsh, say, like in D&D), who blesses everyone with fearsome power in melee encounters. (Again some 5% or smaller/bigger bonus)
Idea is to bring some more lore to the game (Cuz info on god and pantheon is ALWAYS mandatory and interesting in any fantasy fiction. If someone isn't interested in it, it means he's not fan of fantasy at all... seriously, Valars would simply abandon such hopeless soul,) and also some game mechanic, which isn't mandatory but could be considered and utilized by players ahead. I suggest many gods with many bonuses, so it wouldn't get too repetitive and give that kind of feeling before game - "Well, can't wait to see, what blessing will come out this time."
2. Item cards.
I bet idea was considered and told already. But it' simple. Some cards, may be as another section in drop-down (items), where cool artifacts would be captured. Difference is, you pay only gold ('lot of it) to summon weapon for specific squad. After that, weapon can't be destroyed, even if squad is dead and zombies rise from their bodies. So they can be recovered. Their power is left on your side to decide, I won't bother balancing this out. As far as I can see, everyone is willing to buff zombies, not considering simple fact, that soon enough after such buffs, no one will have "fun" dealing with their annoying AI. So, giving more neat options for living souls exclusively is finally something, what should be considered as well. (Don't buff only zombies, livings need some love too!)
Yeah yeah, there are units for that, and some of them even fly. But wouldn't it be interesting, if enough carry capacity for those units with advanced movement, to carry one more person? Say, dragon would carry some 10 brave man. Have bunch of them and you can carry simple squad of orcs. Or strong but less in count units. Idea is stupid. but, well... something interesting. Could be even some way of transportation bonus for races, like chariots for humans and cart-rails for dwarves.