Maybe new buildings or units, "human" or monster like dragoons I don't know... Why not add some troops of goblin in the shop like dwarves?
Some craft in our city? Like some games who you have to craft items for being better or finish some quest, why not some specials stones, wood or pieces of stuff for "updgrade" our heroes?
Stuff can updgrade health, attack, armor, cure, heal, etc... And it will be fun to have heroes with strong armor with dragoon's bone or anything else. Item for crafting this stuff can be droped by dragoons, ogres, battle against other races
Just few ideas but maybe good things and new objectives in long time for "old players".