Very seldom do people report a failed upgrade. There is a lot of confirmation bias and often people who don't even know what good sounds like often report great improvement, often directly proportional to how much they spend and how much they had to drink during the testing.
If they make the report the same day they did the upgrade, I don't trust it much.
Once you have upgraded to high quality cables, I think the difference is exaggerated. I look for real technical differences in the cables I upgrade to. For example I like low mass connectors and super high quality copper or copper/silver/gold allow for analog. (note that allows generally degrade conductivity so if you're looking for higher conductivity, avoid sterling silver which has a lower conductivity than copper. Avoid any alloy. That said, conductivity isn't always the key and Mundorf has done some good research). for digital I like solid silver wire as I think digital has such high data density that the improved conductivity helps. My ears confirm.
Of course I validate with my ears. I never consider an upgrade to be successful until I've listened to it for a week, return to the old component, and can clearly conclude the old component is inferior. If I'm not sure, then I call them equal and this happens more than you might think.
Jerry