Honestly....The answer to increased productivity with stagnant wages is Hispanics. Extremely hard workers, and will work for less money than anyone else. It's not even arguable. They bust ass on any job they do.
That's not a rant. Anyone that says they haven't noticed more Hispanics working the grill/ preparing burgers in the back are lying. Makes for shorter waiting times as well.
Because they come from countries with no safety nets, if you don't work hard, you starve and die. I've rented to tons of Hispanics that show up here with a 1 year work visa and 5 word English vocabulary, yet within a week they already found work somewhere getting paid $100+ a day, living like kings and sending home a lot of their money for their families. Many will work here for 3 years and that will make enough to build a house, a business and be set the rest of their life back home.
The issue is, before most Amercian will go tunnel under a house for plumbing or lifting work, they will go to a McDonalds and load up on all the federal assistance.