I would just be careful about the financial risk assessment. If you're willing to shell out thousands and thousands of dollars for a degree just to get a higher GPA, then that's fine. But you also have to consider what happens if you don't get the GPA you hoped for after two years. Will you view the MPH as a waste if you don't get the GPA you want? Also, were there extenuating circumstances for your previous GPA, or are you at risk to experience similar obstacles? More than anything, an MPH is a lot of money, so you need to be sure it's exactly what you want to do. It could help, but it's important to evaluate why you want it and if it's something you truly want to pursue.