Spade vs bare wire

There is a vast chemical difference between tarnished and a metal's oxide. In a normal room environment, metal tarnishes, so the validity of the oxide conductivity is specious.

Gas tight connections are best. Bare wire in a connector is a poor idea as it will tarnish. Gas tight connections can be effected with crimps, but require the proper tool, connector and wire. Soldered connections may sound a little different, but it is unlikely that the solder is the issue. There can be several dozens of soldered signal path connections in every device.

Worrying about solder when there are likely multiple crimped and soldered internal loudspeaker connections is silly.

A standard speaker connector with a well crimped/soldered ring or spade terminal cinched down with a nut driver makes an almost permanent connection. The two layer WBT are as good and don't require as much torque to keep tight.

https://hackaday.com/2017/02/09/good-in-a-pinch-the-physics-of-crimped-connections/

https://media.digikey.com/pdf/data%20sheets/molex%20pdfs/tbo%20quality%20crimp%20handbook.pdf

AND, AS ALWAYS, YMMV. Any advice not generated in your context is worth 0x0000000000000000000000000000000

This is not the vendor I've used in the past, but these low-mass BFA style banana plugs look like the ones I've used in the past:

https://www.moon-audio.com/bfa-gold-banana-plug.html?gclid=CjwKCAjw27jnBRBuEiwAdjQXDBxSG5U7-ovA8GR2-oQd-blBAuCC1zw1aYl8MB8JBK74ZJb094cC3xoC3HMQAvD_BwE

I typically clip off the crimp wing and solder them to the cable. They work perfectly. They have a large contact area, fit tightly and don't loosen over time.

I gave up with connectors, they corrode, get loose etc. So I solder the wires straight through. You can remove the plastic cover on the back of speakers thus minimizing damage.

“Connectors have their own sonic blablabla” lol what a crock! 

@bac2vinyl
I was once head of analog engineering at a professional recording console manufacturer. When I arrived, my engineers had pretty much the same attitude that wire was wire and connectors pretty much of a muchness.

We made up several identical lengths of a few different cable types with XLR from Neutric, SwitchCraft & Amphenol in both gold and silver.

After I demonstrated that I could reliably detect cable types with the same connector and connector types on the same cable, they all woodshedded to learn how to identify the characteristics. In the end, they were all convinced there is no free lunch.

Note that we were not trying to determine gradation, just difference. Gradation is skewed by system and CBLF.

We went on to recreate a classic EQ, paying attention to 'inaudibles.' The unit has sold in the thousands because it is almost indistinguishable from the originals.