I would say that a college diploma carries less value now than it did 20 years ago.  Here are my main reasons why:

First, we have to understand what a diploma means with respect to the real world.  A university that issues a diploma to one of their graduating students is claiming that the student has completed a course of study, and that the university is satisfied with the student's competence in a certain field.  Unfortunately, that competence is largely rooted in knowledge, and the diploma says nothing about the graduate's ability to think creatively or critically, or even if they could function in a real-world working environment.

Second, the cost of higher education has risen significantly (at least in America) since the 1980s, and student debt has ballooned to alarming levels.  At the same time, the wage advantage that college graduates are expected to enjoy over non-graduates, has failed to keep pace.  Add in the fact that employers have placed more emphasis on skills and relevant experience within this time frame, and it becomes more and more difficult to justify the financial costs of attending college and getting a degree, especially if that degree takes longer than the traditionally expected 4 years to complete.  The increasing number of stories of college graduates who could only find menial jobs doesn't help the diploma's image either.

Third, advances in technology (and in particular the Internet) have brought about alternative (and in many cases, cheaper) means for people to acquire/learn relevant skills that are valued by employers in the modern-day workplace.  Online classes, Youtube tutorials, and other Internet-based instructional materials are for many people, far more accessible than having to physically show up to a college campus for the purpose of learning and gaining knowledge.

Because of all this, I maintain that a college diploma is worth less now than 20 years ago.  I will even go one step further and say that if colleges don't revolutionize by finding ways to cut tuition rates (simply freezing rates will not be sufficient) and be more accessible to the general public, then I believe there will come a point within this century, when diplomas become completely worthless.