While things like "space billboards" would be a good thing to talk about when it comes to anti-capitalism, it's also a little too obvious for it be primary area of focus. I don't think it takes much convincing for most people to see that space billboards are a ridiculous idea. Sure, the prospect is scary, but the truly horrific parts of capital propagate themselves through capillary pathways between people and others and people and the material world. Thus, they'll be largely invisible and require an understanding that goes beyond "space billboards are bad" to instead asking, "what are the processes capital goes through that lead to the possibility of space billboards' existence?"

Basically, "space billboards are bad" is too narrow an idea to focus on if we want to convince people to become socialist. It's still a good idea to bring it into other discussions, though, as an example alongside other things.