I am slightly torn; I understand Catalonia's right to self-determination, and acknowledge the inherent processes of democracy - however, Spain in interfering with the referendum, essentially declared it null - by preventing people from voting, seizing ballot boxes et cetera.
Hence, if possible, the referendum should be run again - with no interference from Spain; in the best case scenario, the administration of the vote should be delegated to an impartial organisation - e.g. the UN, or the EU (though some may state that they are not impartial in their methods). In my eyes, the referendum was just a watered down version of the Venezuela Constitutional Assembly vote which was truly a shambles.
Regardless, it is evident that Catalonia wishes to be independent, so eventually Spain must accept this. Nonetheless, the independence of Catalonia will not work without detailed discussions with Spain on a transitional agreement, and the migration of taxation systems et cetera; it would be a bureaucratic nightmare - i.e. a mini-Brexit; but if Catalonia truly votes to become independent, they should be able to do so.