An MBA will not be enough to get you in the door of an accounting firm in the Audit or Tax fields. My wife works for Deloitte, I have a degree in finance and an MBA, they wont hire me becasue you have to be CPA elgible. There are some areas of accounting firms that being elgible for a CPA does not matter. However, you are stuck there will little room to move.
An MBA will open more doors, it does not keep you pinned into one field. Remember you are only as good as your last degree, so while it is a great accomplishment to get a Masters, do you think it matters to someone in IT if you have a Master in Accounting? I guess what I am trying to get at is, yes you may love crunching numbers but ten years from now you may not.