It seems to work well. Makes an interesting mix between the greater
stability and resource control of land vs. the greater profits from trade.
Perhaps it could use some fine-tuning in future games. There are two
factors that seem to determine the value of a trade route:
profit-per-weight, and % profit per investment, and maximum profit per
trade run. The first is more important for overland routes, the second and
third more for ships. Perhaps they could be balanced more so that
something good in one area is less good someplace else.
Also, an interesting twist would be if the selling price was higher the
farther you went away from the original city. This would be slightly more
realistic, and might also encourage "hit-and-run" traders who sail around
the world looking for markets.
The IM