I don't think there's much question that degrees in general have been dumbed down. And many people are able to get one without acquiring much in the way of skills an employer would value.
In the 1970's a lot fewer people got degrees and thus they contained more of a signal of achievement to employers as well.
I can agree with this.
The reason college courses are dumbed down is because the students that are admitted are "dumber", meaning less college ready. That is for many reasons. One is the overall push to direct all students toward college whether they are capable or interested. Another being the increase in minority students whose readiness by every indicator is significantly lower than their counterparts.
Third, graduating seniors in general are less prepared for college work is evidenced by their steadily lowering SAT scores in verbal, reading, and writing areas (math has stayed rather steady).
Bear in mind that the green "some college" section is people who didn't complete college, most of whom failed or quit, and only a few who got AA degrees that are virtually useless except for a couple specific majors directed toward office jobs like bookeeping. Should we be surprised that barely getting into college, then failing out or quitting doesn't translate into a good paying job?
Also, the lower SAT scores reflect on another fact related to the blue category of people that were dropping out of high school and now are getting a GED. Namely that this has been accomplished by lowering the standards needed to graduate high school and pushing students to get a GED, which really requires no more education that the folks who used to drop out were getting.
As for the dark red group getting college degrees, the degree means less not only because more people have them, but because it is easier to get because grades are inflated because more students are admitted that would fail past standards. Then there are all the for-profit colleges and trade schools being counted that rip people off.
Also, trautsi's point about majors is also valid. The most popular majors have not changed that much. But there are many specialty majors now that didn't used to exist and there is either no market for them or way too narrow a market due to their extreme specialization (just the number of various ethnic and gender studies majors accounts for a lot of economically useless degrees). Then their are majors that did exist but lost or never had value and/or more students take them now than in 1970 (e.g., journalism/communications, general liberal arts, art history, theatre, creative writing, etc..). The influx of students who are not ready for or really interested in college means more students looking for the easiest/funnest route to any degree. These combine to mean that their are more people graduating with the type majors that have little economic value.
In sum, actual education would likely help a great deal in getting people out of poverty. What does not help is handing out more diplomas and degrees by making them require less education and effort or creating educational specializations that have little to no economic return.