Apologies for linking to a Buzzfeed listicle. However, there are some pretty photos here, of what ten writers at the American Writers & Writing Programs conference considered the term 'Successful Writer' to mean. To me, being a successful writer means having lots of readers who enjoy your writing.
Read the pretty pictures here: http://www.buzzfeed.com/saeedjones/what-does-successful-writer-mean-to-you