I agree with you in as far as it makes a great multiplayer element. In the vs the computer game it is a bit of a crapshoot though. Working with different world leaders is not something that is possible. You can't sit there and strategize over several votes. Futhermore the later in the game you are the more frequently they meet. By the information era they are meeting every 10 turns.
Agreed. Against my better judgment, though, I still try to hammer out "diplomacy," or some moderate semblance thereof, in my games against the AI. Mods are almost necessary in doing so, as the vanilla AI and rule set are optimized towards conquest. (Some AI personalities are more treacherous or aggressive than others, but virtually all of them will pursue military expansion over real diplomacy, provided the risk/reward calculations favor their odds.)
Again, I'll have to take your word for the annoyance of this element in Civ5. In Civ4, the UN is the closest equivalent. I found it to be somewhat enjoyable, if inconsistent in its decision making. It can throw a real spoilerish element into the gameplay that I like in my games. For instance, if I'm over-relying on my nuclear arsenal as a source of military power, and the UN suddenly bans nukes, the playing field is leveled toward factions with bigger conventional forces and fewer nukes. I have to adjust accordingly, or else pray that the issue comes up again in another UN session and is reversed. I dig that.