Street sweepers? The German guest worker program began in the mid 50's during a rapid growth in industrialization and a rapidly growing economy. First came the Italians, the Spanish in 1960, it was then expanded in 1961 to include the Turkish, Morrocans, Tunisians, Portuguese, and Yugoslavians. These people worked in factories and mines, they were trained, educated, and well paid. while not without some difficulties regarding citizenship, discrimination. They have made Germany a stronger and better country.  As of March 2016, the unemployment rate in Germany is a record low of 4.2%
 Reunification probably caused Germany more problems, racial tensions are typically far more common amongst those from the former East, I suspect that many from the East sheltered by the iron curtain never experienced the shame/lessons of the War.