My professors warned me about post-bacs before I started applying. They said it was often a way to bleed people for money. The school might get three years of tuition from you instead of two, and at very least one more source of money without crowding their MFA program further. It could make sense if you had a degree in a non-art area or similarly unusual undergraduate situation, but otherwise you're just paying a price as high as an MFA education without the degree to show for it.
NY Time article More Than a Bachelor, Less Than a Master cites Samuel Messer warning students to be wary of post-bacs:
"Samuel Messer, associate dean at the Yale University School of Art, one of the top art schools in the country, takes a cautious view of post-bac programs. Over all, he says, some “are quite good and set high standards, while others take more casual artists.” Yale does not offer a post-baccalaureate but has accepted post-bac participants in its M.F.A. program. Mr. Messer, however, expresses concern that many of these programs are simply “money-makers” for the schools, “a catchall for people who are afraid to be out of school and probably need to just be out in the world, gaining life experience.” "
If you are rolling in money and have plenty of time, it could be worth the boost. Then again, you could also boost your portfolio by working like crazy for a year before reapplication.