the analogy I always draw is to wine.

the difference between a $5 bottle and a $20 is perceptible. but, the higher you go, the returns diminish exponentially unless you have a specific taste... and at some point paying the excessive amount of money becomes status not necessity.

yes, potatoes are conductive, but they don't have any shielding and the distance the signal travels in those experiments is irrelevant to practical applications. it is essentially a big wire nut.

if your application is long distances through conduit or many cables run in parallel you need higher quality ones with shielding. Granted, that is not the typical listener's case.

Not when there's load (like for speaker cables). Turns out shielding only matters for signal cables (which means analog ones unless your digital cable gets so long that it would have real signal loss)

https://www.tomshardware.com/speakers/in-a-blind-test-audiophiles-couldnt-tell-the-difference-between-audio-signals-sent-through-copper-wire-a-banana-or-wet-mud-the-mud-should-sound-perfectly-awful-but-it-doesnt-notes-the-experiment-creator