I have been reading a number of cost benifit analysis of establishing a trade route verses the income it generates. I was pondering this when it hit me! There is a guaranteed way to make income from the trade technologies with no capital investment other than research costs (or trading cost).
Sell it to all of the other Civs!
Some of you will immediately dismiss this as an exploit, but it actually works out quite well. First you get cash or other valuable assets in return for the technologies, which with lots of opponents and minors can add up to several thousand BCs.
A tidy sum in and of itself, but beyond this, eventually, they will start establishing trade routes with you. This brings you a steady weekly income with no cost to you!
Later on in the game you can even convert old ships who have outlived their usefullness into trade ships with little cost (I always have a few extra survey ships floating around.)
Scincerely,
Scintor@aol.com