I agree that directly trading wealth probably doesn't make sense. But minerals and tech seem to be things all starfaring races would value; if they don't, they won't stay starfaring for long!
Now, as you say, there might be issues with communicating tech to other races. Perhaps the more different the race, the lesser fraction of the tech you get? But we can already disassemble their tech for a chance at an advance.
EDIT: The really hard part would be deciding on the 'exchange rate' between minerals and tech. Different techs can be exchanged on the basis of research points, of course.
Probably the different racial traits would affect how hard a bargain a race drives. You also have to be Neutral to have any chance at all, and more preferably Friendly. Having a trade pact would definitely be nice, but not necessarily required.