The sand always gets pretty gross underneath the rocks as well. I had cooked up a scheme for my 140g tank where there rocks would sit on little plastic "bare-bottom islands" kept clean with flow from the closed loop. It unfortunately didn't work as I couldn't get enough flow to keep the bottoms clean.
I think you've got it though; keeping up with snails is the key. I just hated the cost of always adding more snails
A conch is a GREAT way to help keep the sand clean; I had one in my 140g and it was an awesome creature. It would bury itself in the sand and then all of a sudden you'd see a single eyeball pop out of the sand, look around, and sure enough it would surface, vacuuming the sand.
A tiger tail cucumber was also another great inhabitant. Dirty sand went in the front, and clean sand pellets magically appeared out the back.
If you're running a filter sock, at least you can capture the fine sand particles from a storm easily!