Si tenéis tiempo y ganas, la opinión de un inglés: E. F. Schumacher makes a strong case for smaller independent economic units because they give people more power over their own destiny and are fairer. Larger economic units tend to pull resources to the centre and disenfranchise large sections of the population.
If a majority of Catalans want independence then I think their right of self determination should be respected. If Spanish people outside Catalonia don't want them to have independence then it suggests there must be something to be gained by the rest of Spain by keeping Catalonia in and thus gives credence to the Catalan claim that they are getting a raw deal at present.
I'm English but when Scotland votes in a referendum I'll respect their decision if they want to go it alone even though I believe we will be weaker in England because of it. Ultimately, whether it's the UK or Spain, all people forming a union owe it to each other to ensure they are all getting a fair deal and if people want to leave then those left behind ought to examine their own attitudes and behaviour.
It's like a marriage, if it isn't working out for you and your spouse isn't prepared to talk about it or make any changes then maybe it's time to get a divorce.