I didn't apply to any MBA programs, but I have two thoughts:
1) Dual MPP/MBA programs are pretty common. If you have strong reasoning why both would help you achieve your goals, plenty of schools have programs where you can get both degrees in 3 years.
2) Why do you think you'd be able to more quickly pay down your debt with an MBA? I think post-grad income is dependent more on the industry you're in than the specific degree you get, and people conflate the two because people who get MBAs tend to pursue higher-income careers in finance, consulting etc. more often than MPPs, which leads to the perception that MBAs necessarily lead to better-paying jobs. If you've already settled on development consulting as a sector, the jobs that will be available to you probably won't be that different whether you get an MPP or an MBA. You'll probably be making about the same amount of money regardless of the degree you choose because of the industry you want to enter.