Concept Art doesn't have to be revolutionary, but there has to be something unique about it, otherwise there isn't much need of it, is there? So yeah, there's a distinct difference between Fan Art (which is what I assume you've been working on judging by the post) and Concept Art. On the other hand, practising Fan Art is still practise - you'll develop a skill in art that is preferable to have when you work with concept art, because it will allow you to produce what you have in mind.
Good luck!