Your most indispensable "tweak"?

Debrox > Deoxit.

Sacrifices to the Greek God of music Apollo. 

Details of Carbon Fiber outlet cover.....this is the most idiotic thing I ever experimented with.   Surely the replacement of a plastic outlet cover would have no effect on the sound.   I even tried to load the inside of the cover with Blutak....no difference at all, so I left it in place.   The outlets themselves are audiophile approved Maestro, the cable is Neotech with top of the line Furotech carbon fiber plugs on each end.  On a lark, I went to Ebay and got 3 carbon fiber outlet covers for the 3 outlets in the stereo room.   The covers are from HongKong (although they came through California, they were 20 dollars each, and the change was very dramatic all on the up side. 

Annual ear wax removal

Symposium Acoustics Rollerblock Jr+ under my turntable and this all on a Symposium Acoustics Segue ISO platform.  Stunning improvement on bass notes, all percussion, and a wider/deeper soundstage overall.  So much so that I have since added more Rollerblock Jr+ for my other components and now have on order a Symposium Acoustics Foundation Rack Ultra.  I also found very good improvements by adding in a Niagara 1200 power conditioner and NRG wall outlet and am using AQ Tornado power cables.  Then added a dedicated 20 amp AC line.  Then upgraded to AQ Earth signal cables.  All of these upgrades (tweaks, as you may wish to call them) made very good improvements each and every time.  So, had to do another.  Recently went up the ladder in speaker cables with AQ William Tell ZERO.  WOW!  That is one heck of a cable.  Upgraditus is suggesting to me that I am not done.  Good fun, no doubt.