I enjoy having a tall spindle sander but, often what I am sanding is not that tall.
To even out wear on the sleeve, you have probably seen a variation of this . . . I knew I kept the material from that cheap-o stereo cabinet for something. I was able to get four panels out of the scrap. Three about the size of the spindle sander table.
I mark the outline of the table top and drill for dowels. A protruding dowel in each corner will engage the layer below so I can stack the identical pieces for varying height. I mark the "front while they are still taped together in case my measurements aren't perfect and the holes only line up one way . I then glue dowels in that protrude enough to catch the layer below but, not so much as to run into the dowels that are in that lower layer's holes.
The fourth piece is larger. I place two dowels at opposing corners to catch the table top and hold the whole rig in place. I have an early morning and so will finish up tomorrow but, I'm pretty sure you get the idea .
Depending on the thickness of what I'm sanding (or where my sleeve is most worn) I can add or remove layers to change the elevation and therefor the part of the sleeve that is used.