The labor market has to be the overwhelming factor, I have to think. Another way to reduce illegal immigration would be to make it faster, easier to migrate legally. Despite what anti-immigrantion activists want us to believe, there's no "back-of-the-line" to get your papers, so until we reform that process, people will be forced to take dangerous, risky journeys to come to the States.
A new study from the Pew Hispanic Center finds that illegal immigration is down. Annual inflow between 2007 and 2009 was roughly two-thirds less than between 2000 and 2005, report Pew authors Jeffrey Passel and D'Vera Cohn. Furthermore, "the most marked decline in the population of unauthorized immigrants has been among those who come from Latin American countries other than Mexico."