Some realistic ideas (maybe?)
Civ bonuses:
- Stable technologies have a +50% stat improvement but unit upgrades increase unit cost by x%
- Wheelbarrow and Hand cart increase villager work rate by 5% (or less)
- Monks have +1 conversion range castle and +1 imperial (+2 total)
- (Indian camels change?) camels move 10% faster (instead of +1 pierce per age)
Unique techs:
- (Imperial) Infantry / barracks units gain +1 range
- (castle) monks regain faith x% faster (on top of illumination)
- Trade units move x% faster (on top of caravan and dry dock)
- (buff arquebus) gunpowder units get ballistics AND +10% accuracy
- (buff shatagni) hand cannoneers +1 range AND missed shots deal full (or improved) damage