Funny, I just quit the exact same job to pursue my MBA, and also have a similar gpa from tiny, elite liberal arts school. I decided on the MBA for similar reasons - I was pretty stuck and I wanted to open doors in both my immediate future and beyond.
IMO, no, an MBA is not necessary. Another gmatclubber I met once joked something like "MBAs are for people who screwed up somewhere along the line." While I don't think that's necessarily true, it obviously stuck with me. Being a manager or a businessperson or a consultant or wherever you may go probably doesn't require a degree. But the degree may give you a fast track to get there. I decided that a couple years and a couple hundred thousand dollars would be worth the myriad of opportunities I would doubtless encounter by going for it.
It's ultimately, obviously, a completely personal decision. If I were you, I would spend some time researching possible career paths and speaking with MBA alums if you can find them (I had a really hard time with that part - turns out I don't know any...). And if you decide to go for it, consider doing a fulltime program. At first, I had planned to go part-time at a regional school, and the only MBA I found talked me out of it. He encouraged me to aim as high as I could, as it's a once-in-a-lifetime decision and opportunity. Anyhow, best of luck and feel free to pm me .Posted from my mobile device