Here are some small UI improvements that I think would make trading more streamlined:
1 ) Indication of which techs (both yours and theirs) are specialization techs
1a ) Separate markers for specializations in which you have already chosen an option, and those in which you haven't
2 ) Indication for any techs that you can't access in your tree (not sure if this is actually possible at this point)
3 ) Indication for any starbases and/or planets in your ZoI
4 ) Indication of how much your trading partner values each resource/tech (not anything too gamey like a numerical value, just a low/medium/high/will not trade or something)
There's a lot of depth that I'd like to see added to diplomacy, but for now I'd love to at least see the system in place become easier to use.