Blind listening tests have been done over and over ad nauseum. Thomas Edison did his famous "Tone Tests" in 1915 using a live singer on stage along side their recorded voice playing on an Edison Disc player. Audiences often times could not distinguish the difference. His discs, btw, had more dynamic range than today's LPs. Edison was as much a showman as an inventor.
Maybe I am wrong, but it seems like most naysayers are the ones that have never tried specialty power cords and feel justified exclaiming that the emperor has no clothes. Much of the science behind power cords, interconnects and speaker cables has been explained. It takes a good background in Electrical Engineering to understand it. So for many of us lay people, it is more of an art or even magic and ultimately a hit or miss situation. Certainly, the differences made by any changes will affect people differently. Years ago, my wife was with me to do some speaker shopping. What I perceived as night and day differences in speakers were not detectable at all by her. I could not understand how she did not hear a difference and she did not understand why I did. That's it.
I used to laugh years ago at the idea of special speaker cables. Now I have a good sum of money tied up in speaker cables and interconnects. I held off trying power cords until a few years ago. I didn't want to spend the money, but curiosity got the better of me and I tried a power cord on my CD player. I planned to send the cord back and get a refund. The improvement was too good to ignore. Now for the last couple of years, I have been toying with the idea of a power cord for my amp.
Now here is something that I have never found a good explanation for: Demagnetizing CDs. This goes back to the mid-90s. I had read a few things about demagnetizing discs back then and I finally decided to buy a bulk tape eraser to try it for myself. There again, the bulk tape eraser was $25 and I planned to take it back the next day for a full refund. The improvement made to the sound of my CDs was profound. I likened the sound of the CDs to a poorly tracking phono cartridge before demagnetizing them. How that bulk tape eraser can have an affect on something being scanned by a laser, I have no idea. Every now and then I will play a new CD without treating it- just being lazy or just to see if demagnetizing still makes a difference. It does.