I actually just thought of an idea that MAY work, how about there is an option to turn on inflation, inflation would make each of your buildings that generate income produce less income and this effect would increase as the game goes on to convince players to expand (obviously it would max out at some point because of balance issues) I think this would also solve the problem of the player generally having too much money later on in the game. And like I mentioned this option would not be mandatory so that the players who want to take their time with the game can. The biggest disavantage I can think of is that I have not yet thought of a way to make it seem like it fits story wise.
If there is a decrease in the revenue with each built income building, then there would be actually an optimal number of income generating buildings. The effect wont be incentivizing more building, it would incentivize no building at all once u reached that peak point.
So, with no fluff, and no supporting other mechanics, this would actually be the same with limiting maximum number of buildings for no reason. Since cost of each building is same, if profits are decreasing, this result is trivial.
If we are trying to incentivize more buildings, one can think of additional benefits for building more, like diplomacy power etc. Or changing the profits so that more buildings are actually producing MORE profit per building. But that would mess with early game balance, so maybe having some finite resource for starters will solve that.
So basically my counter offer would be:
-No economy can sustain itself in the short run.
-Starting crowns is defined as a lot of more than in current startup. So this bonus will be used instead of actual income from buildings for a while (until economy takes off). Considering there can't be any country in real world with only one factory for income (or bank) that has positive GDP growth, this actually makes sense.
-Objective is making economy sustainable. After a while, there would be again too much income, but that point would be hard to reach until end game.
- One more point. If there is still too much income, just balancing the latter buildings prices would do a good job. So there would be another layer of optimization between spending abundant of money versus efficiency.