So, I have sympathies for the Catalan people, due to historical reasons, in our past 500 years on many occasion independence or acknowledgements of our rights were the central motives of Hungarian struggles. For this reason I have also sympathies for other folks with similar burden all over the globe.
The Catalan situation also relevant for the (still not yet reached) autonomy of Székelyföld (in Transylvania) so they achieving independence would be a huge precedent and might give further strength to push for autonomy.
I think Catalans by themselves don't have a chance. I see two passable routes.
1. Embracing internationalism more. Since they have strong socialist roots this might seem convenient. They should work towards the dissolution of sovereign countries (among them Spain), with the creation of the United States of Europe. However this has the uncomfortable side effect that Catalonia would be relegated under another central government, instead of Spain they would be just a region of Europe instead, and wouldn't mean actual independence.
2. Embracing nationalism, promote Catalan culture and look for allies within Spain. Fan the flames of regional identity all over the country, and lobby for decentralization and placing power into the hands of local, regional governments. Create and nurture the movements in the other autonomous communities, create the powers which could be allied then dismantle Spain together. Basically this would be a self-balkanization of the country instead just leaving Spain. This however bears the burden of negotiating some deal with the EU, ensuring the membership of the newly formed states.