I like the driftwood look. Have you considered keeping a tall, narrow plant like crinum in there too?
You know, I think you could potentially keep some very small nano fish in those, like chilis or other microrasboras. I normally wouldn't keep them in a 2g due to issues with maintaining water quality, but since they have the benefit of the stability of the large tank, you could probably keep a half dozen in one overflow box (assuming the hole isn't big enough for them to escape through, might require the addition of some mesh over the hole). You could still keep small shrimp with them too, since the shrimp would mostly occupy the floor or climb the hardscape.