One thing to consider is that some people have more sensitive hearing than others. If you find yourself NOT hearing tweaks than stick to bigger changes like amp, dac, speakers. If you hear changes in speaker cable then you should hear tweaks that work. I have use Herbie's and Gaia's (IsoAcoustics) and IMO IsoAcoustic products are the best. I use them under my amp, TT, TTmotor, speakers, dac--all with sound improvement. I also switched out to Sophia Electric EL34's--huge difference, BUT, big problem with reliability.
I can't say what would work for you, footers vs tubes, but if you plan to keep your speakers I highly recommend the Gaia's.
As someone else said, speaker placement, and room interaction is very important, BUT, I just did some DIY bass traps and the sound is improved, but it won't tame a (50Hz?) bass problem enough, but does help. I ended up moving my speakers back 6" because Clayton says moving TOWARD the back wall DECREASES bass, and it did.