I'm finishing up my last semester of an MA, and I've found it incredibly beneficial. I was offered a good grant/scholarship package, and the chance to TA in my second year (and i'd been doing the corporate thing for 3 yrs, so had some savings). This made it financially feasible for me, but that is always an individual case, and you will crunch the numbers on your own. It's a huge part of the decision, obviously, and a different matter for everyone.
I knew (from HS, nerd alert) that I wanted a PhD, but being interdisciplinary/cultural studies focused, I had no idea how to articulate or even identify my interests. Also, my sense of theory was shaky, at best, even though I was interested in it. So when people told me "research for fit. Look at faculty bios/work" during my first batch of applications, I had NO IDEA what to look for. The MA has been infinitely helpful in allowing me the space to sort out and learn to articulate my interests. Also, i am proud of my writing sample and generally the work I've produced. The MA also gave me a chance to do more sophisticated service work, attend and present at some conferences, gather stronger letters of rec, etc.
I'm very glad I took the MA offer. It's true that people expect more from MA applicants than undergrad ones, but goodness, if you aren't presenting more after 2 yrs of graduate study, I think there's a problem. I am a proponent of either a 2 yr MA or a 1 yr in which you wait to graduate before completing applications, because otherwise you don't have the chance to actually get any of the benefits of an MA before applying again, but you're still shelling out $$.
Obviously, the less you pay the better. Also, some schools (cough, NYU, Chicago) use their MA students to fund their PhD students. Don't go there!! Everything I've heard is that the environment is toxic and professors don't respect your work. Again, this reduced the benefit of the MA, making it less valuable.
YMMV. Hope this helps.