So much here now to absorb ... but with the wizard's staff, I have come to the conclusion (and this is coincidental rather than a contrived response to the topic title) that it is like a musician's instrument. It does not contain the wizard's power anymore than a violin say contains a great performer's musicality yet they are stymied in expressing that innate ability without the instrument - thus is Gandalf "crippled" at Orthanc.
However the staff in itself is not without importance ..it is not merely a stick and maybe would not be "merely" a stick in the hands of a "layman". I love music, but I was a feeble violinist . I remember that my teacher could make my "grotbox" fiddle sound fab but I could only produce slightly warmer toned squawks from her lovely Italian violin .....
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I am afraid I don't have the "Letters" but I imagine the wizards and their staffs might well have been a subject of correspondence - does anyone know?
On a lighter note - it has just occured that there is a close resemblance between the "tools of the trade" of wizards and Conductors - the wand or baton or the staff .... perhaps it is jsut as well that Gandalf didn't "do a Lully" when he smote the bridge!!!