My idea is essentially the same. Each resource deposit has a certain value (could be 100, could be 150, etc.). It's used up, but perhaps in a more dynamic way; it's a long time ago, but I think the formula involved population. So the more population you have connected to the resource, the faster it depletes. There's been more recent versions of this idea (or threads in which I've found an opportunity to spout it
) and I think I've moved more to it also being dependent on buildings. At the moment, buildings require maintenance. What if, instead of this gold maintenance, you had a resource maintenance (or you could have a combination of the two)?
So, to take a really simply example, if you made a barracks require iron, and you had one city with a barracks and a population of 2, and one source of iron linked up with an initial value of, say, 200. The barracks might use 1 iron per turn, and the population an extra 1 between them. So the resource would run out in 100 turns. If you add, say, an armory, then you might be using 3 iron per turn, and the resource would run out quicker.
It sounds quite complex, but then it's just the same as gold. You have a total amount of gold coming in, and a total amount going out, and you can see the balance between the two, and how much of a surplus you have. You could do the same with resources. How much do you have available, and how much as you using per turn?
You could also add in some cool mechanics with renewable resources (like fish), whereby you'd have to engage in sustainable practices or risk completely exhausting your supply.
What you're suggesting is essentially exactly the same as this, but maybe without some of the added complicated bits. But I don't think making it more dynamic, with more variables, would make it worse; I think it'd make it better.