GPA is fine have a MBA...
Just a word of warning: your MBA isn't going to matter much in med school admissions. (I have one too, with honors from a top school, because I used to work on Wall Street.) Strange as it may seem, med schools give almost no weight to graduate and professional GPAs--it's the undergrad GPA that counts, no matter how old the grades are. Take my case as an example: I never took the premed requirements in college, so I did them in a 2-year postbacc program just before I applied to med school. But those postbacc grades were averaged in with my 25-year-old college grades to compute my undergrad GPA for application purposes. Even if you earned a second BA, those grades would not replace your old undergrad record, but would be averaged in with it.
So, before you make this leap, take a look at your undergrad record to see if you have GPA issues. You can still get into med school with them, but it's a lot harder, may take longer (due to need for additional courses to buff your GPA) and you might not be able to go to school in your location of choice.
Regarding the big picture (is this worth doing), I would say yes--provided that medicine is your passion and you can't see yourself doing anything else. Keep in mind that your plans will require huge sacrifices, not only financial but personal, in that you'll be giving up virtually all of your free time and control of your schedule for the next 10 years or so. (In that vein, I am really skeptical that you'll have much time to spend with your kids during your premed studies and med school, even if you live in the same city. I've barely seen my immediate family for the past 4 years, and we live in the same house.)
If you really have a burning desire to be a doctor, those huge sacrifices will be worth it, but otherwise, I would think twice. This is an incredibly difficult and demanding profession that is hard not only to get into, but to stay in, and it's likely to get harder as health care reform kicks in. There's no reason to put yourself through all of that unless it's the only kind of work that could possibly make you happy.