In my own experience, a master's degree will open doors for you.  I worked in a museum for eight years, and was not able to advance within the museum structure, nor find a more advanced and challenging position when I only had my B.A.s in History and English. With all of the highly qualified and talented people in the job market, a B.A. did not seem to be enough.  I have recently graduated with my M.A. in history with Museum Studies components and although I do not have a job yet, I have been able to turn down a few offers while I look for the museum that I will be of the most benefit to, and will challenge me.  I really think that while experience is invaluable, the education will give you an edge in the job market, as well as the reverse being true.  Of course this also means that you must love what you are doing.  If you go to work in a museum half-heartedly and apply yourself to your education in the same way, no amount of education is going to help.  A person will always receive what they give whether it is in opportunities, money, etc., and it is your own drive to be the best and contribute the most that will help you.