Crystals - placebo effect can be a thing, and if they provide a sense of relief that’s a good thing. As long as they still take their actual medicne and don’t think putting a herring in a sock will cure cancer.
Cables - While there’s obviously a cut-off point. As an IT guy I have fixed a not-insignificant number of issues with sound/display/network quality/dropouts by replacing crap/damaged cables with slightly more expensive ones. Just don’t expect them to turn. a 360p stream into 4k