I think it shouldn't be to difficult to implement a more realistic simulation of economy based on population, demand and supply ... Good examples can be found in some German Trade Simulations like "The Patrician" I+II or "Port Royal" I+II by
Ascaron.
At the moment, the game is treating Europe more like an infinite Reservoir ... You can buy any number of goods without having the prices change during a turn ... the same applies for selling goods ...
Imagine ... you sail into harbor with your treasure fleet ... galleons loaded with hundreds of tons of silver ... in reality the prices would drop immediately as soon as the enormous treasure gets known ... traders would not dare to pay you much for the silver since they know that market will collaps ... so the knowledge of the treasure fleet alone will already force prices to fall ...
In sense of trade-simulation, even if the economic system is not based on supply and demand, the stored number of traded goods which influences the prices should decay over time ...
On the other side I think that the unrealistic trade concept was done on purpose ... High School of Game Design ... the Game is designed to keep you in movement ...
- You can build crosses to get colonists from Europe, but the costs for each new colonist increase until it is no longer worth ...
- You can build universities to train your colonists, but the costs for each new colonist increase until it is no longer worth ...
- You can produce goods to trade with Europe, but the prices will fall until it is no longer worth ... (and taxes will rise, threatening your most traded goods with boycott ... all based on your trade)
- You can buy units in Europe, but the costs for each new unit increase until it is no longer worth ...
- You can produce bells in your cities to raise rebel sentiment, but due to decay of rebel sentiment, the percentage will raise slower and slower ...
I just wonder why they did not use the progressive system for Food-costs for new population and hiring costs for European specialist, too ...
... and for the equipment costs of tools, horses, guns for pioneer, soldier, dragoon ... (e.g. see "Rise of Nations" by Brian reynolds as extreme example of progressive costs)
The game seems to be designed to force the player to not rely too much on a special feature and to not overuse it by making the benefits of all features kind of depleting (using up) when overused ... a market with recovering prices does not seem to fit in this game concept.
Civ4Col (unfortunately) is rather a DESIGNER GAME (like a Card Game) than a simulation of colonial history or colonial trade ...