I use little brass disks sold for just this purpose.
The general idea is to minimize the surface area of the speaker cabinet to the floor, AND minimize the movement of the speaker in space. Woofer's exert a lot of energy and may actually move the cabinet as they play.
So, spikes + mass are a good combination. Are they that important vs. say, flat furniture feet? Not sure.
Adding weights to the speaker top is also something to experiment.
If you can't hear the difference though, it's just a fetish. :)
Best,
E