I know there's a pretty big forum post about trading so far which you can find over here
http://www.arcengames.com/forums/index.php/topic,15399.0.html.
Regardless of how trading is tweaked or balanced, I feel that the information presented to the player regarding trade routes seems a little unclear. Whenever I go to check out the Broker Trade options, I feel a little bit lost as to why trade routes can't be brokered. It does make sense that you can't have TOO many trade routes since there's only so many resources that everyone has to offer or needs.
However, the math behind what can allow a trade route is pretty unclear.
Actually, scratch that sentence. The options that the player can take to help improve the number of trade routes is not completely clear. Based on some quick tests, it makes sense that trade routes are dependent on the income rates of the 6 different minerals, since going about and helping the races colonize a bunch of moons results in new trade routes to appear. However, the ability to compare information to see what is needed to create a trade route is something that isn't quite in the game yet.
I feel that the Race Relations screen is probably the perfect way to do this. Imagine a 'Trade' mode in that view that allows you to see the resource production of all the races. With such a view, the player could see the differences in resource production between races as well as what the player can do to help 'create' a deficit; either by colonizing more moons and promoting mining developments to increase resource production or by sabotaging mines to decrease resource production.
Let me take an example scenario that came up in a most recent game (this is 1.004, excluding the Federation Points addition).
I have a Federation composing of 5 of the 8 spacefaring races, minus the Burlusts who are about to lose their last planet, the Evucks who are close to joining short of a few more credits from my end, and the Peltians. Those fuzzy Peltians don't like me at all, and I need to figure out a way to get them backdoored into the Federation through the Skylaxians or maybe even the Andors. At this point, I can't create a trade route between them and the backdoor-capable Federation races; which would be a great way to get them in. Some sort of screen to put the information out there would certainly help to figure out what needs to be done!