I'm finishing up my MBA right now so here are my thoughts...
If you have a business undergrad, an MBA might be an overkill unless you are interested in healthcare administration. An MBA will definitely open some doors in that case.
If you don't have any business background, like I did 10 months ago, getting an MBA is a great decision. Marshall has one of the top entrepreneurship program in the US so if you're interested in getting business training to figure out how to start your own practice, USC is the place. However, since USC is so expensive, you guys might want to look into executive/part-time programs at UC's. Also, many graduate business schools require work experience before letting you in, so keep that in mind.
I am glad I decided to get an MBA because I had absolutely no clue about business. I admit that it's a lot of common sense, but if you have no knowledge of accounting or finance, common sense might not be enough. If you already have a business background, taking a course in entrepreneurial finance or small business/venture development is probably all you need. Also, I am learning a lot in my business plan capstone project. Great hands-on experience that would be very beneficial for anyone wanting to start their own firm/practice.
Check out the MD/MBA forum and PM me if you have any questions.
Also... Don't sweat the GMAT. Just figure out how to answer data sufficiency questions and the rest is cake.