Silver- gold longtime benefits?

Well, I own some "Mark Levinson" coax Teflon covered wire aquired around 1984. It still is in use in some interconnects i made. That wire is really still nice copper wire with fine coatings still.
It was some of the first 99.999 pure copper wire made for cables.
Then some 1980's (so notoriously bad they became famous) Monster Cable Speaker wires turned Green (or black) and became unlistenable within a few years.
Some AudioQuest Midmight wire, the copper stayed the course, the insulation got strange and the electrical quality of the cable was rotten enough I had to discard the cable.. in less than ten years from new (I shudder when I see 20 to 25 year old AQ Midnight up for sale.. eeech!)
So each wire is it's own chemistry lab. Some last, some don't.
The idea that you're gonna want the same wires twenty years from now is silly. So I would drop the 'everlasting' from buying reasons.
On the other hand, many alloys can do strange and wonderous things...

The advantage of gold is it will never corrode. But its conductivity is rated at .95 where copper is the standard of 1.0. Silver is 1.05. Silver can tarnish where the tarnish is still conductive but resistive too. When cooper corrodes that is an extremely high resistance.

That being said I have a 23 year old pair of copper speaker cables (99.9999%) and although it hasn't corroded yet the copper ends (bare wire) does get discolored. I cut back 1 to 2 inches every 4 or 5 years and all is like new again. Even though I still have those cables I don't currently use them. I upgraded to the Nordost Frey's which are silver plated and polished over 99.999999 copper AND sealed so tarnishing should not be a problem.

Last all metals will sound different so go for the sound that you want. I wouldn't worry about how long they will last.