In general MPP students do not go on for Econ PhD's. The coursework in an MPP is not really relevant. There are a few MPP or MPA programs that do sometimes place students into Econ PhD programs, but we are talking about a handful of programs near the top (Harvard KSG MPA/ID, Chicago Harris MPP, maybe one or two others), and most of those students who went for PhD's had stellar UG profiles.
If you are really interested in an Econ PhD and feel that your background is too weak, you would be better off going for a MA in Econ. The math requirements for a US MA in econ are not that high, typically Calc II and one semester of econometrics with a few programs requiring Multivariable Calc and Lin Alg, and B's will usually suffice as far as math grades go. If you had really poor grades in your math classes, retake them at a local CC or public college and then apply to Econ MA programs. Most US MA Econ programs are nothing more than applied economics for industry programs, but there are a few which are directed at students who wish to improve their profiles before PhD application, and there are some MA Econ programs at lower tier PhD granting institutions which regularly place students into mid and lower tier Econ PhD programs. Regardless, a top 30 Econ PhD will be extremely hard for you to get into, especially with you being 10 years out of school, and needing 2-3 more years to improve your profile. Top 75 is more reasonable, with top 50 being possible but that is still only after you improve your profile.
I think the bigger question you should ask yourself is whether an Econ PhD is really what you want. You are 10 years out of school and will need time to improve your profile. You have industry experience in policy and there are some decent Policy PhD programs that are less quantitative and value relevant experience and might take you with minimal improvements to your profile. Those programs would also value an MPP more than an Econ PhD program would, though I don't know how much more.