Well I guess I should play the regular game at some point
keep asking questions in the general that I think would apply, but clearly do not 
In any case, this is what I've found out regarding trade agreements:
Slave brokering when traded to the AI: Gives them a 5% manu bonus, but no wealth or research bonus that I can see
Free Trade Agreement to the AI: Observed no tool tip bonuses to the AI
Cultural Treaty: I've never taken this pick to offer them.
TO ME
Slave brokering to me: Have not been able to get anyone in current game to offer it to me, I do seem to remember trying it once and not seeing anything, though I may be mistaken.
Free Trade Agreement to me: Observed no tool tip bonuses that I could see.
Cultural Treaty: Works as stated.
Not sure if it is intended that these bonuses stack? Even after concluding a treaty of this sorts with the AI I can offer it to them again (and they to me). I haven't tried it yet as I was fearful of a crash.
Of another note I cant get seem to get Non aggression pacts to pop for the AI (i can still offer them, but I've learned that these are not two ways, both parties have to trade it) even with 'close' relations. Have they been disabled? This is in the late game, so I'm pretty sure the AI must have researched it by now (since they can offer me trade agreements).
I've noticed now the AI won't simply accept Alliance offers now (have to have high relations I'm guessing?) as two cordial AI's would not accept an alliance with me, but a close relations (and weak) AI would accept it. Which is nice.