Hi Stir Frey,
I'm wondering if you ever found out the name of the plant you were looking for.* From your description, plants that come to mind that grow in a ball shape, have thorns or spines and could be a blue color are Euphorbia or Aeonium.* I don't know of any that fold up when they need water though.* There are hundreds of varieties of both.*
Maranta or Prayer Plant folds it's leaves at night but doesn't grow in a ball shape and doesn't have any thorns or spines.
Maybe these folks might be able to help you.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.