Your thesis is mostly correct, but we need to be careful about how the income related data can skew a few things when looking at rural Nebraska:
1. The vast majority of Nebraskans residing outside of Lincoln, Omaha, Grand Island, Hastings, and Kearney work in Agriculture or an Ag related field.
2. We need to remember there is a significant distinction between "Wealth" and "Income."
3. There are thousands of farmers and ranchers in Nebraska who are WORTH Millions and often might bring in less than $50k per year. Farmers and Ranchers can write off damn near everything and if cattle or grain prices take a hit, they can claim a loss even in years where they might pay cash for an $95,000 GMC 3500 Denali.
Where your data really hits correctly is in Urban or Suburban areas. Kids in Gretna, Bennington, and Elkhorn win a lot. That's not just a coincidence. Its because their parents care and their parents have money. Hell, you can even see it on a smaller scale in communities like Pierce, Aurora, and Amherst.