Great game, really neat and interesting.
English is not my mother tongue so sorry if this sound strange sometime.

After playing a little I have few ideas.

-Gold could be obtained with a tavern area . Your minions could spend money on drinking booze there.
Raiding humans Hops farm would bring the material for it. Crops could grow again every x turns

-Would be nice if Monsters get a satisfaction factors. If orcs/ some monsters don t kill/drink they get angry, the more angry they become is a risk to get a riot and a keeper attack.

-other underground levels would be nice. Lava world with demons and dark elves for example.

-Calendar event could be introduced. For example day of the orc would boost +1 to orcs, day of greed would make your minions take  a gold coin in your treasury, some would give +1 to enemies armies damages and spawn a raid etc etc.

Would spice things up if you attack a village at night or defend your dungeon and a day with malus against you just pop on your face.

Like in heroes of might and magic some days could spawn enemy creatures too, like days of the unicorn or day of the elf.

-Vampires once controlled could maybe take human forms and have a rolled chance to enter human fortress without getting caught if speaking with guards. In human forms they could deal 0 damages but could spy.

They could transform into humans only during the night and die if they keep this form during the day. They could not transform back into vampire form until they sleep in their coffin.

They could have the option to kidnap female npc, we could ransom the prisoner for gold. If the ransom fail legendary heroes could raid our dungeons to save the npc. Once ransom and raid fail, the npc dies.

– More variety of wild animals and spawned monsters/guards should attack us out of the dungeon.

-Dwarf dungeons should have more deadly traps, they should have golem statue to defend the base at the entrance.

-Armed caravans could spawn on routes sometime and goes from X to y until they disappear from the map.