Some people say that snails are yet another different type of animal worth including in your tank, but there's a catch: Snails seem to be able to copulate once (if at all), and then lay eggs the rest of their lives, so yes, eventually they become a pest. In this part of the world, you don't buy snails, they come as a freebie (and surely already carrying), in plants and other stuff you buy, and they will eventually colonize your tank.
Ghost shrimp I've had, and they are cool enough to be worth it. Above all, they don't multiply like a virus. And when they get to be 1 inch or bigger, you can actually see their heart beat, and some other body functions!
Mine used to roam the gravel at the bottom, picking stuff from all over and putting it in their mouth. I never saw them cut down live plant parts, although I suppose it's possible. They used to jump on my arm, whenever I stuck it in the tank, and begin cleansing/feeding from it.