I would argue that the valid approach is: build your "perfect" system and THEN optimise it by any number of tweaks. The snake oils are not meant to replace a component upgrade but to complement a keeper. If one still contemplates a component upgrade, the tweaks, since most of them are system dependant, are money / time wasted.
But once everything is in place and the big job is done, I see no harm in trying lifting cables, controlling vibration, trialing different cables and any other number of "tweaks".
I am in such a place. I could afford to go further but I can only have so much in a small room. A decent integrated, a decent DAC, a decent pair of bookshelf speakers. It's not the "ultimate" system but one I am happy to live with and I have no need / desire to upgrade any of the components in the near future.
I am now playing with Stillpoint racks, power cables, network switches and other snake oils not to "upgrade" or "improve" my sound but to OPTIMISE my system, to allow it to perform at its best, unhindered by a number of known issues.
And yes, all of the above make a difference. Good, bad, worthy or not worthy of your money - only one way to find out. Most of these things can be trialled and dealers are more than accommodating, particularly now.
In my book, since this IS my system, anything that makes a positive difference is a keeper and money well spent. And "positive" can be a very subtle thing. People argue about speaker cabinet resonance but the more educated ears can actually hear the rack resonance and, while dealing with that can costs ridiculous amounts of money and the difference is not night and day, I would argue that removing that subtle distortion, wherever it strikes, bass, midrange, treble - depending on shelf material / build, is worth my money, even if it costs as much as my amp.
And that is the point of tweaks. Your system performance is negatively affected by a number of issues - physics, your room, your mains etc. The added benefits of dealing with vibration, bad power, EMI etc can be a cleaner, clearer, undistorted sound, better tonal balance, a lower noise floor, a sound that flows better, more like the real deal and less like a stereo system and which can be enjoyed equally at any volume. Not extra power, not hearing more. Not transforming a NAD into a DD or a Benchmark into a dCS.
Some of the better (read expensive) components deal with these issues directly because high end manufacturers have the budget for better, heftier cases, better isolation, better power supplies (those amps you can't lift with massive transformers / capacitors etc) so I would say that in fact many of these tweaks benefit cheaper components more.
