Increased faction differentiation by allowing faction specific resources
Factions should be given faction specific resources, not just technology and buildings.
Having faction specific crops or farming styles will give a boost to variety. Not only in theme and art, but a change in logistical and automation game play as well.
Allowing a hypothetical oriental faction access to rice and bamboo as food and building resources would create a style and theme difference, but having those resources function mechanically different will provide real variety. Rice could require more water drying up rivers faster. Bamboo grows quickly providing logs at a higher rate for this faction.
Increased variety allows multiplayer opportunities as well. Players playing different factions can trade for luxury resources they do not have. (Types of food, grain, trees, research, blueprints for leisure buildings.) There are Ideas aplenty.
I believe that having faction specific resources will allow for more of the desired variety, and increase the re-playability of the game.