According to the National Bureau of Economic Research, a college bachelor degree is decreasing in relative value to a high school diploma.
The wage gap between college educated workers and those with only a high school education has flattened out since 2010 after years of growth, a result of both a shift away from middle-skill occupations and a weakening of demand for advanced cognitive skills.(Cited by Bloomberg News, sorry, no direct link to it.)
San Francisco Fed economist Robert Valletta finds evidence of skill downgrading: since 2000, there's evidence that college-educated workers may have slid increasingly into routine jobs, and since 2010, the wage gap between graduate degree holders and college-only workers in similar jobs has declined. That suggests there's less of a competitive edge from additional training.
"Overall, the results suggest rising competition between education groups for increasingly scarce well-paid jobs," Valetta writes. "The flattening of returns as costs have continued to rise suggests that college may be an unfavorable financial investment for rising numbers of individuals."
See also, "Want a janitor's job? Get a degree" and "Is college worth the price?"