[Elladan and Elrohir]

I don't believe that Saruman's taunt (regarding the "staffs of the Five Wizards") means that the staffs themselves are very powerful. He's referring to his self-deceit that Gandalf wants to rule everything, and be predominant over all, including the other Istari (he also mentions the Keys of Barad-dur, which would be symbolic of a victory over Sauron).

I think that Gandalf breaking his staff on the Bridge of Khazad-dum is symbolic of his sacrifice. By breaking the bridge, and the staff with it, he is dooming both himself and the Balrog to death, assuring that the rest of the Company (and thus the Ring) will make it out of Moria. I think he knows before he breaks the bridge that he and the Balrog will both die, and he accepts it so that the cause of the Free Peoples will survive. As a result, he is rewarded by being allowed to return to Middle-earth with enhanced power, to lead the cause of the Free Peoples.

That's my take on those two points of this truly fascinating discussion.