I do think that American culture as a whole is not producing entertainment as good as other time periods overall. I think each type of entertainment has had high and low periods, due to the general state of our culture at the time. There may be a relationship between standard of living and entertainment. Also, events like major wars have an impact. My view is that there has been kind of a smoothing out of our culture. Many major issues such as racial unrest, poverty, the Cold War, are no longer with us or are perceived as not as critical. As more people rise to a higher material comfort level and are less stressed about social issues, entertainment tends to reflect that. Our hotbed issues, such as universal healthcare and (recently) gun control, just don't seem to have the same powerful emotional impact as some of the issues of the past.
Also, as regional and ethnic differences diminish and blend together, it also effects entertainment. Call it the blanding of America. Everything is the same flavor , so to speak.
But as far as what is perceived, it still depends on who you talk to. Those who did not grow up dureing the 60's and 70's are bound to have a different view of those years vs. "their" years. I'm not so sure there is a broad, general perception that the quality of music (or any entertainment) is of low quality, even if "we" tend to think so.