Personally, I think that it is rather irrelevant to solving the immigration problem whether illegal presence in the US is a felony, misdemeanor or civil offense. Few illegal immigrants make much money from the process of illegal immigration-the one asset they typically wind up with(if they are lucky) is a Green Card or Citizenship (which is probably worth about $100,000 in today's market).
What is relevant is how we treat those that really make money off this process-and those that cater to them. Employing an illegal alien, renting to an illegal alien, investing in a business that profits from illegal immigration should be deal with on a basis that make them highly unprofitable. Now, that alone might not solve the problem-but the tendency of Mexico to export its poor rather than uplift them can be dealt with:
The US could make it clear that without better education and health expenditures and containment of private fortunes in Mexico, NAFTA will be nullified. For $60 Billion/year all extreme poverty in North America could be eliminated. The excesses of the wealthy in the US and Mexico can be contained. Illegal immigration can be reversed—and it doesn't have to mean deprivation for the poor in Mexico-or even the illegal immigrants in the US.