It's hard to say with confidence whether or not the snails are doing damage. I lost 2 plants since then - a mini orchid and a tillandsia, but it also could have just been that the conditions weren't well suited to them - I think that is most likely, actually. As I'm considering expanding out to some nicer/pricier plants and plan to break the tank down anyway, it seems like a good time to fully eliminate the problem if at all possible.
Here's one I just pulled:
From another post here, it looks like this is Zonitoides arboreus.