It seems to me that there needs to be a much more detailed system for domestic demand. Most of the attention I have seen is on fixing the supply side by making factories/rails more expensive or decreasing goods available. I think that what is equally important is to develop a more flexible system for what the domestic economy wants and is able to pay for. Demand should be dynamic and capable of rising to meet any level of prosperity.
As it stands the population seems to have a hidden pool of money available to buy a certain amount of goods and no more. I suggested in another thread that there should be a way to influence wages. Favoring low wages would concentrate wealth with the elites giving you more capital and greater demand for luxuries, while high wages would create greater demand for staples and allow for greater social mobility. Either way it should be almost impossible to make everyone happy. If the player represents the political and economic decision makers, there should be a lot more influence over the relative power of the different social classes.
Regardless of how it is accomplished there needs to be a system where demand is more responsive to what is going on in the game. There is no way a country would have large stocks of livestock, wine, and luxury goods sitting around that no one wanted. If your factories produce all you need, you should be able to pass reforms to shorten the workday, either by law or custom depending on the type of economy. It should be possible to play as the US or Britain, spend the entire game focusing on improving the standard of living, and never max out the potential.
In the long run I imagine this would be much easier than trying to calibrate the game's production to be optimal for a pre-set amount of demand.