@tomic601 Brings up a good point, and that is that a lot of spades and the speaker connectors are not given a lot of thought.
Focal for instance used nickel plated binding posts, which is a very hard material. Using it with hard spades results in a situation where they will never grip for long. This is why we assemble machine screws with split ring washers, so the spring keeps the screw tight. No give, no reliability.
WBT makes what I think are the most reliable spade connectors, which use a type of spring to ensure the spade and post stay tight.
Yes, it's true we want maximum contact area, but have you ever taken apart a female IEC (power) connector, or wall outlet? The actual contact area at the plug is very small, comparable to the contact area of a good banana.
Lastly, solder is never used in high current installations like power transmission for a reason. It's brittle and doesn't conduct all that well. Cold well and tight crimps are the way to go.