In this CBS news video, the Iowa caucus has cast a spotlight on soaring Iowa farmland prices. This has not translated to a booming local economy, as they report that the general economy in Iowa and job growth are both hurting.
As farms get larger, small communities continue to die, younger people can't afford to begin farming, and the rural residents drive farther for groceries and goods and to find work off the farm for that second income. The "ethanol" boom has not contributed significantly to Iowa job growth. As you can see in this video, the environmental destruction and lack of wildlife and biodiversity that large scale farming has led to contributes negatively to this region's appeal to the younger generation.
But, you say that Iowa's unemployment is "below the national average". This is and always has been true in all of the Midwestern states because of the brain drain. Younger people don't stick around long waiting for jobs to appear. They move on to better climates, to urban areas.
BBC news did an article describing Iowa's challenges and conditions which also paints a rather bleak picture of Iowa, "Iowa caucuses: What excites voters in the Hawkeye State?"