Damn it Nick, withal of this talk about hammers and vibrators I had to pull the top plate off of my B&W stands and check the sand level. And wouldn't you know it, the level has dropped to about 1/2 inch below the top. I guess after playing them over the years the speakers vibrating (especially the bass) facilitated some additional seismic settling. Now that little 1/2 inch gap in the sand should not really make a significant difference on a 28 inch columns, but I know that this is going to bother me until I get the time to top them off.
This does make a good point thought that any of us who have filled sands should look at them every few years to see if normal usage has cause any more settling. I think I am going to add this to my list of regular maintenance items and look at the stands whenever I do periodic things like contact cleaning and system demagnetizing.