While I love the little nassarius snails, the larger size nassarius snails (think drsfostersmith call them "Super-Tongan") are absolutely awesome. I added one to my tank a couple months back and he does an absolutely bang up job keeping the sand bed stirred up. Once I get back to that LFS
that has them, I'm going to add 4-5 more. If you have semi-deep sand bed (and if I remember your pictures correctly, you do) I'd strongly recommend several! Those, trochus, and astreas are wonderful little creatures in my opinion. And if I had it to do over again, I would've only added one or two crabs, just for variety - not the 10 or so I started with.