As a current JD/MPP student, I tend to agree with most of your views. I started my program as a MPP candidate, and then applied to the law school. I am not a law student that plans on just being a regular lawyer, and I would not recommend the dual program in such a situation.
Cost is certainly one underrated consideration. I've actually worked full-time for my current institution for the past two years, and will be moving out of the part-time program at the end of my second year. This has allowed for tuition remission, meaning that I have not had to pay most of my tuition bill. Since I will be moving on at the end of the semester, my final debt load will still be $100,000. Still a nice chunk of change.
If you want a JD/MPP, you likely want some sort of policy job. You can do most policy jobs with either. The biggest difference would be in an area where you needed legislative drafting skills. This isnt the sort of position that you would need the quantitative background. If you were an Econ major in undergrad, forget about the dual program (unless its cheap). MPP tends to be a lot of the same skills, especially econometrics and economics. There are some policy classes in law school, and you can take electives on other campuses if you choose.
I have no regrets thus far with my choice. I plan on working for a committee in Congress, and only having two years worth of loans is a lot different than four years worth. Policy jobs tend to not pay terribly well, even with a JD. Do not let the argument that you will get paid more with a JD sway. And think long and hard about the debt load.
