I've had Dynaudio Confidence C1 Platinums in my 272+XPSDR>250DR system for almost three years now and never bothered to add sand to the stands until yesterday. On Dynaudio's advice both stands were filled 2/3 to 3/4 full with "play sand," a product designed for sandboxes that has been washed and dried. I expected some tightening of the bass, and that's about it. The actual result, however, was both extremely pleasant and unexpected: not only is the bass tighter, but it goes lower with more force. Even better the speakers exhibit greater dynamics and clarity from top to bottom, with better imaging and PRAT.
While not quite like getting "a better pair of speakers" the increase in SQ is far from subtle, I'd say about the same in degree, although in different effect, as adding the XPS to the 272. These benefits were completely unlooked for, but no less welcome for that. So, as the headline says, if your speaker stands have the facility, "Don't forget the sand!" It's worth a try, at least, and at no great expense in time or money.
(Incidentally I was advised, also by Dynaudio, to NOT use lead or steel shot as it could give rise to ringing or unbalanced resonant responses at some frequencies.)