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

@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.

Tinning is probably not the best idea:
 - Solder is soft and malleable, so connections tend to loosen over time and are thus not gas tight.
 - Tinning should be done in a solder pot
 - There are 2 dissimilar junction instead of one
 - Unless you are expert with proper tools and the correct solder, you run the risk of a 'dry' or incompletely wetted flow which are sonically awful.

Issues with oxidation, if they exist at all, can be dealt with a periodic clean once or twice a year.

Pray tell, how do you clean multi-strand 12ga 7x24x34

Besides, concerns with any oxidation of speaker cable pale into insignificance compared to oxidation of cable used inside amps, speakers, the mains, the power station etc etc.

Soldered connections are gas tight and don't oxidize.

Tremendous improvements in sound quality can be effected by removing ALL crimps / headers / connectors from the audio path and soldering the connections

cd318:
Back in the 80s, I became design engineer for a newly built private recording studio. We had identical MCI JH-24 multi track recorders. As best we could tell, they differed very little. Note that we had first rate, phase correct tri-amped monitors, so playback was pretty pristine.

Having auditioned connectors for a couple of decades and finding 'none' better than 'any', I removed every connector from the console to the MT rack cards: Patch bay -> console connector -> machine wall plate -> MT input -> MT rack cards.

Once completed, we tracked some sessions simultaneously to both machines. No one but myself and the owner knew there was any difference in the two paths. On playback, all but the owner and I were astounded at the increase in clarity, detail, punch, etc. IOW, Tremendous!

I did several other studios after other owners heard the delta.

Look inside your typical gear: One may find connectors to/from the power supply, input connectors, switches for Bal/UnBal/Bridged operation, etc. Many fall into the "Best connector you can buy for under a quarter" class and are definitely not HiFi.

Having the luxury of multiple units in the studio and the ability to A/B modified against not, no connectored device ever beat a Un!

NOTE: Only the qualified and competent should attempt hardware modifications.