Regarding silver/bronz contacts:  Silver is used because the oxide of
silver is also a good conductor.  The bronze contact bar does not
deposit anything on the silver side that interferes with a solid
connection.  You may not have to replace the spring silver wires in
your console unless they are worn through and breaking.  The contact
between the silver wire and the bronze bar DOES  wear down the softer
silver--it is intended to wear, an is known as a wiping contact.  The
friction wipes dirt or any kind of build-up off of the contact points
with each press of the key.
  Another metal known for its spring properties as well as being a good
conductor and lack of corrosion is beryllium-copper.  For some reason
this kind of contact has never been used in organ building, to my
knowledge.  I know those years in the Metallurgical Lab would come in
handy some day.