A particular tweak or mod may work for some people, and for others it's a waste of money. What tweaks did NOT work for you?
My list includes tube dampers, rubberized vibration isolation (similar to Vibrapods), "audiophile" outlet, and "upgraded" subwoofer cables. The stupidest thing I ever did was varnish the inside of my speakers so the sound waves would not get "trapped" in the microscopic crevices of the wood. :o