Hey Kate,
I went ahead and got my MPH from SDSU before I started med school. I just felt like i needed something more than "average" undergrad grades (3.25 if i remember correctly) and "average" MCAT scores (9's/10's), to help me stand out. I also worked in research (academic and county public health) for a few years after grad school, and i think that may have also made a difference. If your considering grad school as an option, I say go for it. It'll allow you the opportunity to improve your CV for both med school apps as well as residencey apps. Let me know if I can help with any more info...
Greg
MS1 WUHS-COMP