I’ve been to Mexico quite a few times, mainly down the Western side. I think the infrastructure has improved but only in response to increased tourism. This of course is purely from my own observations. Ultimately though what separates the US and Mexico is the rule of law and property rights; it’s this liberty, which allows prosperity to flourish, although the left is trying as hard as it can to remove these benefits from the US. There is a moneyed class in Mexico that benefits from the status quo and the judiciary, the police and the military support them.
Check out the GINI index for Mexico which shows the income of the top 10%.
http://www.nationmaster.com/graph-T/eco_inc_dis_ric_10
As you say they are primarily economic migrants and whilst I can sympathise with their desire to live and work in the US they cannot expect preferential treatment and they must be made to abide by immigration laws.
On the whole I think the US already has plenty of cheap labour, the importing of more has stifled innovation, especially in agriculture. Consider the advances made in cotton production after slavery was abolished, the same thing would happen in the harvesting of many of California’s crops. A nation that put its flag on the moon is more than up to the task of developing cheap lettuce harvesters, probably through advances in robotics.
As I told my lefty friend, we need to stop importing unskilled labour and start exporting liberty.
How about if we kick our own deadbeats off welfare and let them earn their keep by taking the jobs these Mexicans are doing.