here is how i view 'everything'. 8 years ago, i had been in my dedicated room for 11 years. over those 11 years i had made various changes to the room, but even through those efforts all was not settled. then i happened to visit a friend with the same gear as me, and heard some things about his room that opened my eyes to my own room. which gave me a reference point in my mind.
which got me thinking. two months later i was ready to act.
looking at my ceiling i wondered if i was getting a reflection from it that was obscuring clarity. so i took some cloth i had, and thumb tacs, and attached it to that spot on each side. and listened. better. listened for two weeks. ok, this was definitely better. then i tried it in the center area on the ceiling, even though the geometry was not obvious to be solving a direct reflection. again better immediately, and also after another two weeks of listening. this then started a process that caused me to travel around my room doing this trial and error. cover the surface with cloth, then listen for 2 weeks. it was like finding a door to another level deeper of musical truth, opening the door, then finding another door behind it, opening it. then removing the wall, and finding another door.
i came to the center skyline diffuser on my wall behind my speakers, which had been there for 5-6 years and had helped calm my center image. i wondered if with the treatments i had done whether this was still helping? was this now a wall in my way? i removed it. better, listened for two weeks. still better. added cloth on that center round diffuser. better.
came to my two front windows. 5 years prior when i removed some bass trapping i had the contractor build window inserts. however; at that time in my room development i could not tell the difference between in and out musically, i liked the view, so left them out, upstairs in my attic.. but now with greater clarity in my room, would i hear a difference? would it be positive? i installed them, much better, more filled in seamless soundstage. covered them with cloth, even better.
both the skyline diffuser and window situation had worked in a previous reality, but until i solved other underlying issues, the benefit of fixing those was not possible.
i was working on my side walls and experimented with many things. eventually i realized i had a resonance between the large side surface of my bass towers and my side wall, and added some t-fusor diffusors to that area. but i could only localize the issue since i had added some much more clarity.
at the end of this process i discovered i could hear the reflectivity of the meter bridge's on my Studer tape decks since they were at ear level to my direct right as i listened. i covered them with a towel, better. that was something not audible 9 months prior. now everything was revealed to matter, since the other issues were no longer covering them.
i've not touched my room acoustically since then, 8 years ago. it was a lot of work, but i've loved it since and had zero thought of messing with it.
my whole point being that everything does matter when you start to get the room out of the way of the music. but many times in spite of much effort there are things in your way so you cannot really understand cause and effect. this same process works on the power grid, the signal path, listening position, speaker set-up, etc. etc.
does everything matter? how deep do you want to truly look? not everyone is willing to look that hard. but that does not mean it all does not matter. you might have a number of layers of stuff in your vision clouding whether things matter.
you do need a reference point, and you do need to believe your ears. otherwise, you will never even get started.