The only real purpose of filling stands with sand or kitty litter is to lower the center of gravity. Which is great for stability. I personally do not buy into the idea that a Speaker can generate so much energy as to make a steel pipe ring at a frequency you can hear. The thing about filling a stand is that you want to make certain you aren't putting anything in it that can corrode or rust the metal. Kiln Dried Sand is often recommended for this as it has the least water content short of getting Lead or Brass Shot. Kitty litter is Clay which will contain moisture. Salt is corrosive. Speaker Stands should only be filled about 2/3 full to avoid raising the center of gravity too high.
Now... because it was brought up:
Spikes couple to the floor and are meant to punch through carpet and set firmly into the floor board. This is where you get stability from.
To properly level such a stand, you need to get it sitting solid, then incrementally level it by adjusting all of the feet. I have such a VTI stand and it was kind of a PITA. They are pretty stable now, but any 3' stand with a 32# Speaker on top of it is going to have some play.
Regarding the top plate. Museum Putty is a good solution. I use a monitor isolation pad between my speaker and the stand, but I also needed the 2" the pad added to the height.
Everybody freaks out about the dimensions of the top plate. It's not worth the energy. Get the stand level and sitting firm on the floor, get the speaker protected so it does not get scratched, make certain it is sturdy enough to resist a drunken attempt to hug the Speaker... that's about all you can do. My wife bumped one of my speakers and it slid on the pad a bit. But stayed upright.
Now if the old San Andreas decides to give out, I don't think my BMRs will stand a chance up there on those VTIs, or any other stand.