Almost all calculations done on the viability of Catalonia as an independent state discount the possibility of a drop in GDP caused by the changeover. Catalan nationalists cherry-pick economists who agree with them, but some financial institutions have estimated Catalonia could lose up to 37 billion euros if they break with Spain. 
Catalan separatists have not factored in the debt they would have to pay back to Spain, the cost of a Spain-Catalan border on export revenue, and whether or not they would become a member of the EU.
The central government has listened to Catalonia's complaints about the deficit in infrastructure spending and agreed to do more to ratify the problem. An extra 4 billion euros has been promised to fund the Catalan rail network. 
Claims that Catalonia will run their own institutions better than Madrid on the basis that Madrid has recentralized local government are false. Although the Spanish government has interfered in the region, Spain is still one of the most decentralized countries in the world according to the OECD. 
Catalonia already does run itself. A bid for independence is both expensive and unnecessary. Complaints about infrastructure spending have been heard and addressed.