Agreed, decriminalization and/or legalization is the most logical solution,
it's working in Portugal so it should in theory work everywhere else.
Better education and infrastructure in rural areas is essential to prevent the brain drain, which should in turn improve economic conditions in the area, in turn improving opportunities.
One of the issues that you have left out however is how the American agricultural economy functions. Because the price of food is kept so low (comparative to Western Europe for example) only large farms can survive and these large farms make massive usage of economic seasonal migrant workers (illegal or otherwise) that work for very low wages. By and large locals of a rural area will understandably not want to work for wages that low, so while there are often plenty of 'jobs' in rural areas, they are pretty crappy.
The migrants that do such jobs usually do so for only as long as they can save up enough money to afford a decent living in their home country or until they find a more permanent job somewhere else in the USA with better pay + hours.
Don't get me wrong, these migrants are not the main problem. While they are taking jobs from locals, the vast majority of locals would not want such low paying jobs in the first place. The bigger issue is big companies like Walmart that drive the prices of food so low to the point where farmers have no choice but to rely on super cheap migrant labor, resulting in a lack of economic opportunity for locals in the agricultural sector unless they already own farmland.
Here's an interesting piece addressing some of those issues from the perspective of a former child migrant worker;
http://www.cracked.com/personal-expe...er-in-usa.html