I enjoy the open concept and the ability to kick someone out of your turf....or to be kicked out. Must keep in mind that this is not Civ. There are quests to do and that means crossing other factions territory. I don't really like how harsh some factions are when you try to cross their territory. Understandably, if I'm headed for one of their cities, they should want to respond. But if I'm just cutting the corner of their empire...I should be able to get away with it, to set up an agreement that allows me to cross for the 2-5 turns needed to cross...
Open boarder agreements are great....and they exist! In the form of non-agression pacts. The 50 turns is too long sometimes and not long enough in others. Imo, the turn limit should be variable and partially dependant on your relation to the faction and partially dependant on what the faction is trying to accomplish. Thus, the weight of such a trade can be different as the game progresses.
Closed-border agreements are an interesting concept. Essencially boycotting another faction. Naturally, if you boycott someone, odds are they'll boycott you. This can lead to embargos as the faction's allies are beginning to share fated decisions. I would definately be for such an inclusion, including the chance that boycotting a faction (like Kraxis) could all of a sudden find yourself completely shut in. Oops.