Most Effective Tweaks?

Wondering what generic tweaks people have tried that made the biggest difference?    Also interested in how much the tweaks cost to implement and the magnitude say from minimum of "marginal" to maximum of "transformational".

My top tweaks I can think of so far are

1) isolating speakers from versus coupling to floor when needed  (~$100, transformational)
2) Mu metal shield around low level  phono stepup transformer ($30, transformational noise reduction)
3) power cord upgrade (significant, ~$80)
4) acoustic panels (significant, $90)
5) power conditioner (significant, $100)
5) Physically moving components further apart from each other (NC, marginal)
4b9c724a 509c 4bb1 a384 a61b6782a9d0Ag insider logo xs@2xmapman
I realize this will probably come across as argumentative or beating a dead donkey, nevertheless what I’m actually referring to is not EM or RF. I’m referring to the induced Magnetic field from the transformer or in some cases from adjacent AC cords. That’s why wrapping mu metal around a transformer improves the sound, because the mu metal absorbs the magnetic field. Mu metal has nada to do with shielding RF or any such thing. It’s also why it’s a good idea to avoid parallel runs of any cables or cords. In some cases the 60 Hz hum is due to the physical mechanical vibration of the transformer.

Most Effective Tweaks?

Fuses are the most effective tweaks.....   price/gain ratio  is by far the best. 

the music you play #1
room acoustics positioning  and treatment DYI mostly.  transformational
speaker cables significant
speaker stands, points,  proper coupling and isolation (I use both right now) significant to transformational
Green pen the edges of your CD's center and outer edges (very significant to transformational) $3.00
Acoustical damping components (marginal to significant.
Arcicci Levitation rack, Billy Baggs rack significant.
Acoustical damping front wall between speaker   dense tapestry  Significant
acoustically damping components  DYI marginal but noticable
Closing eyes and darken the room significant 
then going deep into music nirvana  HUGE!
a good contact cleaner.
and probably (not yet fully tested)  tweeter diffraction (felt etc) , rings etc
and I am voting with Synergistic Research or this; Sun spots take you sound down a whole bunch of notches,
my experience, when I lived in Seattle, is that in damp cold fog  your system will sound dead and flat.

Tube dampers another effective and inexpensive tweak.

Mapman wrote,

"Tube dampers another effective and inexpensive tweak."

Yes, they are. As long as they’re Herbies tube dampers. I have tried all the others, including the very dear Swiss tube dampers from Ensemble and while it took me a long time for it to dawn on me, they all subtly hurt the sound. It's a case of it just seems like such a great idea, of course they couldn't HURT the sound. All of them save Herbies. It’s a lesson in how easy it is to over damp things. And for my prized ’52 Badboys and ’42 Tung Sol rectifier two Herbies were the cat’s pajamas, one on the glass at the location of the getter and one on the base, even though it should be pointed out the cost of the dampers can approach or exceed the cost of the tubes.