I am doing much the same with my Vandy VLR's, but on some wall mount speaker clamps.
I, too, wondered about the effects of vibration on the speakers, as they aren't really tightly held in their clamps, so I asked Mr. V.
He suggested to touch the sides of the cabinets. If they aren't moving as much as the nearby wall, then using any additional isolation shouldn't make much difference.
-Mind you, I was considering bolting my speaker cabinets to a rigid wall/ceiling mount that would allow me to adjust their positions.
In any case, I did do as he suggested, and my speaker cabinets showed little vibration at the volumes I listen to, so I probably won't be changing their mounting.
Bob