This seems like a weird place to ask this, but whatever.
I also have a few acquaintances that went the PhD route, one that worked with USAID for several decades as an agricultural economist. I have also studied HR/labor policy and can speak to that in general. However, I am at a rather low point, professionally, so take this all w/ them grains.
-Geography: I hope you like NY, DC, and living out of the country because one of these locations is probably where you’ll work. If you are interested in the military aspect of it (most / a lot of USAID projects are associated with the military) you also have a chance of living wherever a major base is located; in this case, security clearance may decide whether or not you’re employed. There’s also a chance to work at a state capital, but you won’t need a PhD in econ for that… it’s knowing state regulations and being a more of a lobbyist.
-Development: Local and international don’t really overlap (Comm can overlap with ID, but not much vice versa). Local/community development is, well, local by nature and helps if it’s someplace you grew up and have years of contacts with; you do not need a PhD to do this… a BA will suffice and even that isn’t necessary if you know the right people. Economic development is a little different; you definitely need a BS, but it’s more sales than anything else and a degree in public relations will probably help more than economics on a local level, but a lot of work can be done internationally on the PhD side.
-ID: It’s pretty divided into doers/implementers and analysts. If you’re interested in a PhD, it doesn’t sound like you want to implement. It definitely helps if you speak another language, particularly one of the standard languages of the UN. If you don’t naturally speak one of these, realize that a lot of the world speaks their native language and English, so you need to compete with these people. The field, in general, is also very competitive, so I hope you like to network. The UN also tends to hire people for limited amounts of time (3 years), suck up their expertise, and release them. The US Feds have a policy where you can leave your federal job to work for the UN and come back to your job, so this may be worth looking into as the USDA is the largest employer of economists in the world (they also have a booklet describing what economists do at the USDA somewhere on their site)
-public policy: it’s a very broad degree, with people going into high level econometrics, BI, operations research type stuff to more sales (US economic development = a lot of poaching big companies), community development, or programmatic work. It can compliment other education quite well, but on it’s own, a BS doesn’t seem like it’d get you much, though probably more than international relations, due to its quantitative nature. It’s also not a common degree, so nobody knows what it means. Most will interpret it as public administration, which is then interpreted as a lazy version of an MBA.
-MS vs. PhD: Anecdotally, I’d say the PhD folks seemed happier. This could be due to their acceptance of a long program, less of a rush to cram as much stuff as possible, disposition, or who knows, but they didn’t seem as stressed out. However, and I know at least one person like this, if you are really smart and a good communicator, you can get a PhD level job with just an MS; I’d imagine this is true in many fields. On a purely economic level, a PhD is not worth it; time out of the work force and other factors will yield lower lifetime salaries than just an MS (though, as a good economist, that just tells you that the utility derived from people pursuing these positions compensates for the decrease in income); this varies by field, but is true in general. A PhD is also more likely to restrict your options geographically.
-Outlook: You can check out the BLS and do your own research to really find out, but here’s my general observations. There is currently a federal hiring freeze, so it’s tough to land a federal job (this is particularly true if you aren’t a veteran), and a lot of econ jobs, esp. international, are federal. Locally, I think an MBA would help more than public policy because people at least know what that is. Also, with the growth of online education, unless you go to a top school, you’ll probably be competing with someone that was working fulltime and taking classes online, so they’ll have several more years of experience (you can decide for yourself whether or not the education is at the same level) and most government jobs only require the degree and don’t care where it’s from or how it was obtained (not the case for consultants). Lastly, a lot of unis have programs where you can extend your undergrad by an extra year, concentrate, and pick up your BS and MS in 5 years… most folks I’ve known that have done this used it as a stepping stone to get a more standard MBA or MPH… I supposed this could also be used fora phd.
I’m tired of writing.