Too much college, but it pays
The "too much college" thesis holds that, from a college-as-job-preparation perspective, there is a society-wide irrationality in the amount of people we expect to earn college degrees. Many of the jobs that college graduates take do not actually require a college education to perform successfully. By creating an expectation of universal college attendance, we waste people's time, generate frustration among people who aren't good at formal academic learning, and run up huge student debt.
Now consider the causes of the college wage gap. Certainly a good portion of it is due to the fact that certain higher-paying jobs really do require higher education. There's really no easy way for someone to become a good lawyer, nurse, or engineer without some type of postsecondary education.* But another significant portion of it occurs because employers use college credentials as a screening mechanism even when a college education doesn't actually make you better at the job. Imagine you have an opening for a receptionist. In this economy, you might easily get 500, or even 1000, applications. There's no way you're going to carefully read them all and give each person attention to the nuances of their qualifications. You need a quick and dirty way of chopping the pile down to a manageable size. Screening for a college degree is an easy way to do that.
The core of the "too much college" thesis is that college credentials -- both the official diploma as well as the cultural capital (mannerisms, etc.) acquired during college socialization -- are used as employment criteria even when they're not materially relevant. Yet it can remain perfectly rational for individual employers to perpetuate this irrationality, when 1) the job is not one that puts a high premium on having the absolute best individual employee, i.e. someone that's "good enough" is nearly as valuable as someone who is "totally awesome," and 2) screening based on credentials is far easier than trying to assess directly job-relevant skills.
Likewise, a college education is still potentially a totally rational choice for the individual job-seeker. From a social perspective, more people getting degrees doesn't improve anything -- it just shuffles those college-degree-job earnings around to different people and piles up more student debt, without increasing overall social productivity. But from the perspective of the individual job-seeker, getting a degree means getting a shot at those jobs that you might be perfectly good at but are irrationally barred from due to your lack of a degree.
I realize that it's dangerous for someone who works as a college professor to endorse any aspect of the "too much college" thesis. However, I would counter by pointing out that "too much college" gives a partial picture by focusing only on college as a job preparation mechanism. I think college has a much broader value, for example in personal growth and preparation for citizenship. I have the one job that most clearly requires formal college education as preparation -- and yet I would also say that the most important things I got out of my college experience (undergrad and grad school) were not what I learned in the classroom or how it prepared me for a job. Indeed, my first job after getting my PhD was one (newspaper copyeditor) that I could have done successfully straight out of high school (barring any irrational degree screening by my employer!). Unfortunately, the pressure in the world of higher ed administration is very strongly toward reconceiving college as a pure job training program.
*Though even there there's wiggle room -- law school for the most part doesn't really teach you any useful information or skills for lawyering, and it's possible to be a successful autodidact in most technology fields.