I'm a believer in getting the big stuff done first. That would include "audio infrastructure" (to me, speaker placement is included within acoustics).Cellcbern talks about what I call audio infrastructure: electricity, vibration, acoustics. These seem like basics to me. They may be called tweaks because so many come to addressing these after they've plopped a bunch of gear in their room. Perhaps if we knew then what we know now we'd pay attention to infrastructure as a starting point rather than as 'fix'.
Over the past few years I'm more engaged in getting rid of those sorts of tweaks than acquiring them. It is probably heresy to most -- but there it is. Stillpoint Ultra 5s under my Alexias and other footers - gone. Noise reduction wires - gone. Thirteen acoustic panels in my room - twelve are gone. Power distributor/conditioner - gone. My de-tweaking allows musical energy (vitality, vivacity) robbed by those tweaks to return to my room. Still rolling tubes after all these years; I suppose thats a tweak.
I've found that the tweaks one uses changes as the audio infrastructure changes. For example, once I had the power and network side of things sorted out to my satisfaction, I ended up using different acoustic panels - ones that both reflected as well as absorbed sound. I had learned that I like a lively sound because it sounds more like the live experience to me.
At the same time I became fussier about the changes in sound I was trying to accomplish. Little changes no longer interested me. Only significant changes in musical engagement (not sound, per se) now interest me. Just my own temperament at this point in time.