Usually when we talk about snake oil it's because some one is out to make a buck on the gullible. In the case of these tweaks I want to recommend I'm not going to make any money, and you may not spend any either, but I find them useful.
Cover your Speakers
I don't know why a modest change in your acoustics can make such a difference but I usually find that covering my speakers adds a lot of air and room ambiance. I like to use some thick curtains that I've had from a house a long time ago. Works really well.
Weigh Your Speakers
I don't mean put them on a scale, but put a weight on top. Of course, this doesn't apply to those with behemoths. I find this especially useful with lightweight speakers that are on stands or very small footprints. Think 2-ways, both bookshelf and floor standers. I think the additional weight resists the tendency of the woofer to move the box back and forth, creating a kind of Doppler distortion in the bass. In some cases I find this tweak can really make a speaker sound tighter and clearer from the mid-bass downwards.
Clean up the Floor
We often pay attention to the walls, but not the floor, especially behind speakers. I find that room treatment, cushions and blankets here can really cut out hash I didn't know I had.
