What do you hope to accomplish by getting the degree?
I have an MBA. I am currently working on my MS in Accounting. I got my MBA with an emphasis in accounting to be able to sit for the CPA exam. I came from a non-accounting undergraduate major and an non-accounting professional background. So, in addition to the credits needed for the exam, I needed something business relevant on my resume.
I made sure to overlap my classes, I took the core MS of Accounting courses as my MBA elective. Going into my MSAC I was already 70% done. I am in CA and having a MS in accounting satisfies the accounting study breadth of the licensing requirement. This is ultimately why I went on to do my MS.
If you don't have a real need to get a Masters, I would say don't. I don't think it really adds too much. However, if your employer is willing to pay for it and you feel that it will help you get ahead, then you should consider it.
Both degrees are not necessary. If you want to go into business operations eventually, go with the MBA. If you want to go the accounting director route, go with the MSacc. If you don't know then don't waste your time and money (at least until you can figure it out).