Suggest new ideas here.

I had the same thoughts. Changing seasons:
Winter - reduces growth in all castles, except for snowy ones, and reduces movement speed by 10% for everyone, except for snowy races - like dwarves and ice elves.
Spring - increases movement speed by 10% for everyone, except for snowy races, and increases growth in castles by 10%.
Autumn - evil races - Necromancers and Demons - receive a 10% movement speed bonus.
Summer - neutral monsters appear more often, and everyone gains more experience. And other similar bonuses.

Or, for example, wind in sea voyages. But, in my opinion, all these things are a bit unnecessary. The game is already great, and introducing such things will lead to unnecessary complications.