You might find this article interesting [1]. Although free tuition caused enrollment to rise 22%, still German "university graduates earn 40% more than those with a vocational education." And "making tuition free hasn’t led to any noticeable change in the demographics of who goes to college," partly because living expenses aren't free.

[1] Jon Marcus, "Germany proves tuition-free college is not a silver bullet for America’s education woes" https://qz.com/812200/is-free-college-possible-germany-shows...