Hi!
335 turn route
Do you realize most games are over before the minifreighter returns to its home planet? Also, in 6 and a half game years there are many events that will simply cancel the trade route: Pirates, Peace keepers, assasination, "war has expanded", ... Income from trade is simply to risky money to rely on it building an extensive network of trade-supporting starbases, and lose all the investment due to a random event.

Unaugmented trade in my games usually brings from 1000BC to 2000BC. Importance of this amount entirely depends on my economy: if I run an empire of 100 planets, it's negligible. If I have just 5 planets, it's a game-winning tool.
There's also another nerf to the trade: when your treasury increases over 10,000BC, the trade revenue of all routes is halved. Like the game isn't enough MM-intense.

Now I look at a trade just as a diplomatic tool with some small financial bonus, and I really stopped worrying.

BR, Iztok