If you just want to learn economics and practice it as a vocation, then you can learn outside of formal university settings. You can read on your own and participate in various educational program such as the Mises University and Mises Academy.
http://mises.org/events/184/Mises-University-2014
http://academy.mises.org/
Graduate school earns you a credential that can be helpful in various career paths. But graduate degrees are not essential to learning economic thought.
