3. Is the relative prosperity of South Dakota compared to North Dakota due to its more pro-business heritage until the latter's rightward turn in the recent decades?
Assuming such a gap actually exists, I'm not sure how long the relative prosperity gap is going to last, given the vast discoveries of oil and gas in the Bakken formation of western North Dakota. North Dakota has weathered the recession better than most states.
But I think your underlying assumption is already incorrect - 2009 median household income was higher in
North Dakota than
South Dakota. South Dakota has more Indian Reservations - or at least more of the state's land seems to be on reservations than North Dakota.