OK, Rhodium is off the list.
Presumably the copper needs a periodic Deoxit wipe. I have done that before when using bare wire to degunkify.
Looks like it's "Hi-yo, Silver, away"!
Bananas rule, spades drool. End of discussion.
I just checked my speaker connections. All using bananas, all nice and tight.
The number of times I’ve had spades get loose instead though.....
Point is, and it really is kind of a tongue in cheek thing, bananas beat spades for long term reliability in almost all setups. If you have to use a Cardas or Mundorf speaker terminal to ensure your spades stay tight it kind of proves my point.