Most useful tweaks that are sensible and really make a noticeable improvement

gillatgh, ….."Ps. Did you know rubbing bacon grease on your cable ends or connectors will eliminate any sibilance in all applications?"

gillatgh, that is ridiculous, haven’t you been paying attention to Geoff regarding the degradation in CD sound due to stray laser music signals? What you need to do is coat your CDs with the bacon grease. You can experiment with plain, maple or hickory smoked to determine the best impact on sound quality based upon your musical preferences. Personally, I find the hickory smoked most pleasant with jazz recordings.

Feel free to eat your bacon after completing the "bacon grease extraction tweak". As with all tweaks, we all know you need to have a very resolving system to hear the sonic improvement, so if you don’t its because you have a mid fi system. My audiophile friends with golden ears and 400 years combined experience are all amazed by the sonic improvement this tweak provides, but mostly only comment thereon after eating the crispy bacon byproduct. You can thank me later.

Ahh yes a new possibility,  never thought to give that a go. Wonder if it'll sound as good as it tastes.
Have to wait till tomorrow as I already disposed of the bacon and the grease for today.
I think I'll market the excess grease to audiophiles. I'll be rich and able to upgrade then. Maybe modify the formula to purified bacon grease.

gillatgh ... with all due respect, your introduction to the topic doesn't fall under a tweak category, more under basic rules for achieving good sound.  Long time hobbyists would begin with great isolated electricity, then follow several of those suggestions as a lift off-off point.  Linn turntable's  Ivor Tiefenbrun, of course, asserted primacy "of the front end," a legitimate argue.  Once that is sorted out, and assuming the components have enough ability to expose sufficient resolving power, minutia and prat of a great system, tweaks can indeed prove fun, and quite beneficial towards one's goals and flavors.  If, however, you are in the camp that find wire upgrades, tube rolling, isolation and the like nonsensical, then, as with religion, no proof will suffice;  for believers, no proof necessary.  Free tweaks include leveling your gear - micro changes to loudspeakers, both vertically and horizontally (search info on bass nodes) - try live front wall, dampened real wall - address ceiling tuning if feasible - Marigo tuning dots skillfully applied to drivers, speaker baskets & cabinets of all sorts...see my responses elsewhere.  Experiment, be playful with it!  More peace, Pinthrift  

An obvious tweak is reversing interconnects to see which direction sounds best. In fact, there are a lot of things one can do to tweak interconnects, just to focus one one thing. Cryo them, freeze them, demagnetize them, apply anti-static agent or device, apply a smidgen of Cream Electret to the jackets, clean contacts, apply Graphene contact enhancer, elevate or suspend the interconnects to avoid vibration and static electric fields. Keep interconnects well away from power cords, at a minimum keep interconnects orthogonal to any power cord. There are even other ways to improve the sound of interconnects but alas, they are beyond the scope of this discussion, at least for the time being. Maybe later. 🤫

@geoffkait, I somehow fail to see the benefit of placing anything between points of contact such as graphene contact enhancer. In my simple mind a direct touch between contact points logically would provide the best contact. One would not place a graphene impregnated piece of material between contact points.
I do however agree with some of your other assertions.