Since this game is going to have vehicles and such, what about a resource that can store energy to be used for work? It could be a chemical battery that needs crafting, but I think it would be more fun if it was a crystal battery that is mined and has value. Otherwise we will need a chemistry skill tree. Although the question of how much energy it should store and needing to recharge comes up.
Iron in turn can form power lines, but why not have wireless charging? Lay the wires in the road itself and it can charge nearby objects. Like what Tesla did with light bulbs. Cars could be powered by a current in the road which itself is powered by public utilities, increasing the need for cooperation. The cars could go off a powered road, but without being in range of a current the battery would deplete.
If instead of cars being single objects, but functional parts, we could use the same machines for other purposes. Instead of the wheels pushing a car forward, they could be attached to boards to push water upstream as a kind of resource conveyor belt for distribution of goods. Maybe I could have a boat road.
Programmable tech like they have in Minecraft would also be nice.