I've been playing Prince recently, winning pretty consistently while doing absolutely nothing regarding diplomacy aside from clicking "NO I DO NOT WANT A FUCKING DECLARATION OF FRIENDSHIP LEAVE ME ALONE" and accepting one or two research agreements when I've had the gold to spare.

Open borders I consider to be an overture of the other Civ towards locating my cities (yes it would give the same benefit to me, but the fact you then cannot launch a prepared sneak attack makes it pointless). RAs are useful very occasionally, but otherwise seem to be a way for enemy civs to take away gold for little benefit to myself. Declarations of friendship meanwhile I see no point in whatsoever. They don't prevent wars like the old Civ 2 alliances did, they don't really do shit actually other than just have the AI whine like a bitch when I don't give them gold on a whim.