A few comments on diplomacy.
On the diplomacy screen, when viewing all of the major and minor races, it is very cumbersome to figure out which civs will talk to you for trading and which ones will not. If you get a new tech and want to trade it to other civs, you have to try talking to each civ to see if enough time has passed since your last trade. If you are playing with 20+ civs, it should be obvious why this is a problem. Perhaps put an icon on their planet on the diplomacy screen indicating they are will to discuss trading.
AI trading suggestion: There are several items which the AI seems to overvalue. Trade resources seem highly valued by the AI, even if they already have the trade source that you are offering. (They get no benefit from having 2, since they never seem to trade away their second.)
AI minor races also seem to overvalue the exploration treaty. (The one that lets you share what areas of the map you can see.) Since the AI does not go very far beyond their home planet, it seems they should not be as interested in seeing what happens across the map.) They will give tons of credits for this treaty.
Offering credits. Annoying that the initial offer is too high, the next is too low, and you have to offer several times before you find the upper limit of a fair trade. When requesting credits be added to a deal, always make the default the maximum that would keep the deal at a fair deal.
Offering credits per turn. Similar to how immediate credits are offered, consider having a default amount near the fair range as default.