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)