I was told to put Kitty Litter in my new speaker stands. Was he joking?

Yes, I used unscented kitty litter in my Skylan stands, 3/4 full. You can use sand, I don't think it makes that much difference. The point is to create some mass. 
  

Do not use kitty litter if you live in a humid area. The litter will absorb the moisture and clump up making it difficult to empty and could corrode the inside of the stands. Sand can leak out if the welds aren't perfect. If you use sand, make sure it is dry. I use small pebbles or pea gravel. They pack in very well if you shake the pillars during filling and easy to deal with if you need to empty. Available, by the 40lb. bag at most home improvement stores. Make sure they are dry too before using.

I've used kitty litter on some stands with very good results. The stands I had used thin aluminum tubes with glass plates on top and bottom. They had a distinctive ring to them when you tapped them and this came through when the speakers were playing. The kitty litter in the tubes completely eliminated the problem. Dill makes an interesting point about humidity. I haven't looked inside the tubes since filling them so I can't say if there are any clumping problems. I don't live in a humid climate but if you do that would be something to consider. You might leave some kitty litter out in a tub for a few weeks and see if starts to clump together on it's own. 

Its like this everywhere. There are guys who say use peanut butter to recondition the black rubber trim on cars. Some monkey says it, some bird parrots what the first monkey said, eventually whole flock of sheep baaa-baaa-baaa-ing the same blather.

All because using the old noggin, ow makes my head hurt. 

So it has been. So ever it shall be. Participate or not. Choose wisely.

go to a pet store that has fish, they will sell clean and dry sand, small pee gravel etc. of various sizes pick the one you like. I've used the sand many times with good results.  if its not sealed along the bottom run a bead of silicon around the bottom area simple and easy.  pet stores have a variety of sized gravel you can use if sealing for sand isn't practical. better then kitty little, wont attract moisture and will be denser then litter and will be cleaned and sanitized (more or less).