Leaf litter would make it look a little more full. However, it is a PITA to clean up. When I had my 90 gallon blackwater tank set up, I covered the bottom with Indian almond leaves and everything looked great. Until the leaves started to break down. Stuff got into the sand that I couldn't ever get all of it up, it kept clogging my python, and the sand ended up looking stained brown/black in some areas. Whenever I would stir up the sand to loosen up the leave mulm from the sand to clean it, I could never get all of it out of the water column (had an external sump with a filter sock to catch stuff), so it would settle back down and make the substrate look crappy again.
I think it would look kinda cool if some java fern or anubias was placed on the driftwood in a couple spots. But then again, I don't know if your geos will eat them.