Tier 1
A) Chopping down trees yields more coins
B) Hunting deer yields more coins

Tier 2
A) When you destroy a peasant camp in the forest, 3-4 beggars will jump out!
B) For the next 5 days, a beggar will come out of your base camp in the morning

Tier 3
A) All villagers convert to militia and will defend your base if enemies get too close
B) When a wall falls it will explode dealing damage and pushing back enemies

Tier 4
A) Walls have more health
B) All your character have +1 health

Windmill
Farmers drop more coins

Blacksmith Statue
A: Builders move faster
B: Builders build faster

Stables
Black Horse: Keeps accelerating so long as you are running
Blue Horse: Has infinite stamina

Large Tree:
Drops 2 wood that can be used to upgrade your base to a wooden castle

Stone Quarry:
Drops 3 stone that can be used to upgrade your base to a stone castle