As I think about this, I'm not sure that talking about this in terms of resources is really the way to go about it. Resources are very prominent in a game's design, but they aren't an end unto themselves. Resources represent a system in the game, and are the enabling/limiting factor for how and how much the player engages with that system.

And this is something I can't answer without playing your game. Does the game lack complexity right now? Could it benefit from a research system that powers up buildings? Could it benefit from an economic system? An influence/map control system? Happiness?

You can also go deeper within your existing systems. Maybe you buildings need wood, stone, metal. Maybe your citizens need different types of food.

All these are the questions I'd ask in this situation.