Fuses, some Power conditioning / or power cords, better capacitors, room acoustics, and certain isolation components do yield results in systems that are musical, and high resolution enough to warrant them.
However, a $50 dollar plastic dot, or a $300 dollar "Wall Harmonizer" are complete jokes, and a huge waste of every ones money.
2 categories of tweaks exist -
1 - Fundamental Tweaks
2 - Voodoo Tweaks