Yes, you are right, one could measure the wave form input with the wave form at the end of the cables, I hadn't thought of that. I was more thinking of the aural experience, some humans might prefer the more distorted wave forms. Shielding apparently is a "thing", for some.
I bought the wife a sound bar with a wireless subwoofer a while back, the wireless connection would pick up ambient distortion fairly often, lightning was one item. I can see that an unshielded wire could pick up ambient foreign signals.
I personally would not spend money on high end speaker cables, but obviously they exist, and some do. As I say, if you invest say $50 K in the system, another $2K is not inherently out of balance with your budget. My system is more in the $4 K area, which I think just about maxes out your return.
For most folks, I think a half decent sound bar is a good way to go for TV/movies and even music in general.
My wife also has this tiny speaker she uses for streaming fairly often, it looks like a gimmick, but as long as the volume is fairly low it's really adequate.