I've rarely, if ever, have had problems with spades loosening in 50 years of using them with half a dozen pairs of speakers. Hardcore audiophiles remove their speaker cables to clean the connectors periodically, so that's an opportunity to tighten whatever connectors are used. Aside from that, I don't mess with my speaker cables, and I have no problems. That was true even when I had two spades on each end to accomodate biwiring.
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.