IMO, an option on the Diplo page is very different from a random event, and UP votes are just a subset of random events in GC2 because you can't do anything to prepare for an upcoming vote, much less try to influence what the next vote might be.
Your starbase-sharing idea seems like a very reasonable complement to the existing Econ and Research treaties, and more options in that area would definitely help 'balance' the basic game bias in favor of war wins--it's an additional relationship you could establish to help bring Close relations with another civ, which you must have before you can propose an Alliance.