Wow, you certainly are more decisive than the average Grinnellian.
You should:
1) Look in the course booklet they send to all prospectives (You can also find courses offered online, Grinnell Homepage > Academic) and look at what sort of classes they offer in terms of the kind of development you are interested in--don't look just under GDS, the only way to know is to look under all the disciplines.
---ALSO, look at the major requirements for economics.
2) If you come to Grinnell, ask an economics professor.
From my experience here, I can tell you that I think the Economics major is very very flexible. If you take one economics class a semester, you'll fulfill your requirements for the major. There is a HUGE emphasis on the international perspective at Grinnell (NO international economics concentration, but I really don't think it should be a problem, you will get plenty of international perspective). Calculus I is the only math requirement - although if you plan on Economics grad school, econ profs reccommend you complete course levels
at least through Linear Algebra. Basically, the major is as mathematical as you want to make it.
AND, you're right that GDS here is focused on the developing world. In my opinion, that's where we should be focusing
Will Grinnell help you achieve your career aspirations? absolutely! Although remember that liberal arts education generally means GRAD SCHOOL.
P.S. I think the music scene here is great!