A bit ranty, but I must admit I agree with a lot of it as well.
A number of years ago I had several different mid-priced interconnects from Audioquest (£30 - £150), which were all an improvement on the scrawny freebie type cables I was using, but the differences between the Audioquest cables were negligible, if any, although a mate and I convinced ourselves one (i.e. the more expensive one) was better than the others, mostly in the bass. Then a few years back when I was feeling a bit flush and having recently bought an entire new system (not sure why looking back, the one I had sounded pretty good) I pushed the boat out and bought an Audioquest Anaconda interconnect from the US that would've retailed for around £800/m I guess (I was in New Zealand at the time). When I got it I remember not being able to hear much of a difference between it and the much cheaper Audioquest cables I already had (yes, I did buy it blind - more fool me).
To serve as a further reminder of my folly, I picked up a Merlin interconnect for about £30 last year as I needed another cable (I sold the other Audioquest cables I had a few years back) and being a glutton for punishment did an A/B test with the Anaconda. There seems to be a slight difference between the two in favour of the Anaconda (slightly smoother treble), but I could be imagining it. Even if there was an improvement, is it worth £770 (probably closer to £900 in today's money)? I'd say not.
I've had similar experiences with speaker cables. Years ago I moved from some inexpensive generic decent gauge multi strand cable to some chunky Audioquest speaker cable (Crystal 2) and couldn't really tell the difference, but ended up buying it anyway, because I was convinced it must somehow sound better. A few years later I bought some Nordost Blue Heaven, which from memory sounded a bit brighter/more detailed but with less bass than the Crystal 2, but not necessarily any better. I ended up selling the Blue Heaven when I moved to the UK, but kept the Crystal 2 as it wasn't worth selling. I still use it now, however I have just bought some QED Revelation (it was half price and I was intrigued if it would sound any better given all the positive reviews) and found there to be distinct difference - not better or worse, just different. The QED cable sounds brighter/more detailed in the top end but the Crystal 2 has more body/mid-bass - similar to the experience I had with the Blue Heaven. I know I'm not imagining it either as my girlfriend who I made sit through an extensive A/B test with me agreed she could here a difference, describing the same sonic traits I experienced even though she didn't know what I was changing in the system and had no idea which was which (other than "the first one" and "the second one").
In terms of power cables, last year I bought a Copper Line Alpha cable, again out of interest, and I can't hear any difference when used with my amp or DAC.
Based on my above experiences I've come to the conclusion that once you've satisfied the minimum requirements of using a decent gauge/quality cable (this doesn't mean expensive), cables can't improve the sound, but may alter the character of the sound (or possibly more correctly alter the way the electronics perform/interact with each other). Possibly, the cable materials may contribute to this as well (a complete guess on my part) - I think both the Blue Heaven and Revelation are silver plated, although I don't know why this should fundamentally make any difference if any.