As of yet, there is not much trade nor room for trade in general (trade ports are just credits generators, they don't trade anything). This game is really more like supreme commander than civilization, more CNC than settlers.
We have 3 basic resources that are being pumped every second into the coffers. There are no tools to trade, no goods. One could trade techs, but could it really be so that someone can pump HCs with zero military labs while the other dude makes five , researches the unit and sells the tech? Even then, it's a one time transaction.
As for diplomacy, there really is not much point behind diplomacy, other than not having to do stupid random missions. I believe it's just so players can cooperate with AI (i.e. make the AI do what it should to help) better. We all know this game is about nothing more than just wiping the enemy. There is nothing in this game that doesn't help in combat, in one way or another. Even the culture is just about protecting your planets from loss to enemy culture, recolonization, for taking out enemy planets and, oh, increase in resource income so you can build more combat ships.
There is just no incentive to do anything other than kill the enemy, take his worlds, rape his women, select the next enemy, rinse repeat. You either are foes or you are friends. You want him dead or you don't.
Oh well. We gotta wait and see. I have a feeling that adding complex diplomacy to sins is more or less like adding an option to discuss politics in Quake 3.
Just please balance this game, cause it's hardly playable as of now (in a competitive sense)....