I never cared, but I do care about the image they are projecting of my country (specially as someone living abroad). Moreover, they are doing great getting the worse of everyone.
I never liked nationalism (including Spanish nationalism) and now it's worse than ever. And I do not like anti-riot police, and I do not want my government to close web sites, and I do not like to see Barcelona burning, and I do not like the hate I see in the eyes of the independentists when they talk about Spain, neither I like the hate I see in the eyes of some people when they talk about the Catalan independentists or even about Catalonia. And I think I could accept all this if it was for a good reason, but I think it is just stupid nonsense (did we learn nothing from Brexit?). We should be moving forward towards some kind of United States of Europe, and worrying about doing something with all these people from Africa who keep coming here, not about breaking apart and stupid flags. I get many questions from friends from all over the world, and I do not know how to answer them, I just feel shame. That's why I care. If tomorrow the Spanish state disappears and we just become one big European country, I would not mind at all.
By the way, you are right about what would happen if an independent Catalonia joint the EU. As a wealthy region, they would have to pay. However, why would the EU allow to join a wealthy country who just decided to break their own laws in order to not subsidize poorer regions?