Almost all calculations on the viability of Catalonian independence discount the possibility of a drop in GDP caused by the transition. 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 considered the debt they would have to pay back to Spain, the cost of a Spain-Catalan border on export revenue, and whether 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. For example, Spain promised an extra 4 billion euros to fund the Catalan rail network.
Claims that Catalonia will run their institutions better than Madrid because 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 globally, according to the Organization for Economic Co-operation and Development. 
Catalonia already runs itself. A bid for independence is both expensive and unnecessary. Complaints about infrastructure spending have been heard and addressed, despite secessionist rhetoric.