Marginal Cost

In economics, we are always looking for the marginal cost in each one of our actions and decisions. Sometimes, it is easy. Sometimes the marginal cost is monetary and other times you have to delve a little deeper. In Civ, we are forced to look at this concept on a turn by turn basis. Each time that we decide which technology to discover, what our workers need to construct or which military unit to train, the marginal cost of this decision will have an impact on the rest of the game. Obviously, if you construct a lot of buildings and wonders, then your marginal cost is the deficiency of your military and vice versa. But, the more difficult marginal costs to consider are the workers and what they build in each given category. For instance, what is the marginal cost of building a longbowman in 4 turns instead of a rifleman in 13 turns? The rifleman is much stronger and is a better military unit but is this benefit worth the longbowman unit and an aqueduct that will keep the citizens of your city healthy whether fighting a war or not. How about the marginal cost of building a wonder that will give you added benefits over other smaller and less beneficial structures? Example: you have the opportunity to build Broadway, which provides you with 5 hit musicals, but it takes 24 turns. You could also build a university, observatory and a hospital in 26 turns. Which situation is most beneficial for your city and your civilization as a whole? Marginal cost is very important in real life and in Civ and much like in real life, it is often ignored.