Over on the GalCiv III Steam page, I asked players to post their saved games so I could check them out. And what I've been finding has been amazing and horrifying simultaneously.
I don't have save game available to show you something about diplomacy, but I'll try to describe it as best as it can: it's kinda broken.
Imho, an Alliance implies you have open borders and non agression pact. But right now, if you have good enough relations with a race, you can offer them Alliance + Non Agression Pact + Open Borders + Research treaty + Cultural Alliance , etc and they will all stack up, giving you a better deal for techs or money.
that is an exploit.
I think that the way it should work is a) you get an Open Border treaty and once relations are good enough and that treaty is expired, you can either renew it or expande to a non agression pact. Not both. Non agression pact implies your ships can freely travel through one's border, not just that you'll stay on each side of the border and look at each other with googly eyes. IRL, it could be a strech, but for the purpose of gaming, I think it's acceptable.
In the same vein, If you are allied, it's implicit that you have open borders and non agression pact. What's the point of being allied if you don't want to use each other's territory and line of sight? I could envision alliance being harder to achieve to compensate that they give more.
And when we are discussing research/trade/cultural agreements, while having one does not preclude the other, right now, it's way too easy to exchange this for multiple techs from the AI as they all stack. I think, right now, it could be that the first of these trade you offer gives you a certain benefit, but when you stack others, they give less&less return value.
Just making it harder to get something from the AI could create an handicap to diplomacy, but at the same time, leaving it like this is way too easy once you start investing in diplomacy instead of weapons right away.