The strangest tweak that works well is the Shakti Holograph room treatments. Don't ask me how or why they work, but I heard a Demo at CES and was amazed at the improvement in soundstage, focus and resolution. Weird stuff, but as I said, it works. They'd rotated the top section back and forth, to demonstrate fine tuning capabilities. They also would remove them and cover them, which showed even more what a difference they'd made. Snake oil? Not if they improve the sonics of your system.
Just my 2 cents.