I'm no expert on crops grown for direct human consumption as that is outside of my specific occupation. From what I do understand, I can say that I'm of the opinion that highly processed, industrialized food is cheap but not necessarily in our long term health or economic best interests, once as many factors as possible are considered. I participate in the production of indirect human consumption commodities (corn and soybeans) not because I have a burning desire to play a role in Food Inc., but because there are no other viable alternatives in which I can reasonably expect to see to my financial stability and that of my parents -- responsibilities that require caution and already entail great annual risks.
I cannot speak for vegetable growers in the Midwest or anywhere else, nor can I speak for livestock producers anywhere. But grain producers like myself have a lot invested in specialized equipment and procedures that in some respects lock us into a cycle of typically narrow margin, high production grain agriculture. There are theoretical incentives to diversify into other crops, but little opportunity given the combination of a lack of marketing opportunities and the high investment costs of purchasing additional, highly specialized equipment, assuming such equipment even exists. Most vegetables are not planted, grown, or harvested via machinery, but rather by hand, requiring a large, expensive labor force. Which doesn't even mention alternative crops that would not produce anything marketable in the first year, reducing income while simultaneously demanding more input costs. This is very risky in the best of years (which cannot be predicted) and potentially financial suicide in the rest.
As fuel and transportation costs increase I do expect to see more Midwestern land go into vegetable crop production so that more food can be grown locally. But the drivers here will be economic, not ideological. As food gets more expensive and the margins for growing field corn become even more narrow, the profit per acre growing vegetables will rival field corn, making a partial switch to "alternative" crops much more likely. But until then we are unlikely to see any major shift in the Midwest away from field corn, soybean, and wheat commodity production.