Kris,
Thanks for the update on this. Â We'd be happy to correspond with folks at JPL about TopoFusion. Â I don't imagine that TopoFusion has increased the server load any more than, say, Earthviewer. Â In fact TopoFusion use is probably a tiny fraction of it.
In any case, it is not surprising that it was the image data, not DEM. Â DEM files are really just 16 bit images just larger than the standard tile (200x200). Â A screenfull of landsat tiles will eat up more bandwidth than three or four 3D views.
So, caching DEM data will not have much of an effect on the overall server load, but you are right that it's one more reason to do it.