A Mssters Degree is a qualifier in the hiring process and also in promotion but I don't think it's at the top of the list. Other factors, such as quality of work experience, personality, and networking ability have a much greater impact in today's job climate.
As a sidenote, one of the greatest takeaways one can get from the MBA/MD experience is the quality of contacts they make. Learning how to leverage those would be much better than relying on the extra line under 'Education' in your resume.
I think it would depends on the degree. I don't think masters in liberal art degrees are any helpful. It seems to me, and correct me if I'm wrong, that the only reason to get a masters or PHD in a liberal art degree is so that you can become a professor yourself but since you only need 1 professor for a couple dozen students, then inevitably, not everyone is able to become professor. This creates the ultimate pyramid scheme.
You don't need a master's degree. If anything right now that may hurt you because you are perceived as expensive. What you really need in today's economy is to be great at something. Good enough isn't cutting it right now.
As a sidenote, one of the greatest takeaways one can get from the MBA/MD experience is the quality of contacts they make. Learning how to leverage those would be much better than relying on the extra line under 'Education' in your resume.