Alas, the Mozart effect has been shown to be, well, nonexistent. As for the Flynn Effect, there are a lot of variables there: for one thing, they are constantly changing the standard IQ tests. They say it is to make them harder, but I'm not so sure.
As for the idea that intelligence has declined, I just ran across a much more detailed study that seems to have discovered that IQ has declined 13.35 points since 1889. This is based on a study of reaction time which is considered to be a good proxy for IQ. Here is a link to that study.
I'm only mentioning this so I can make the modest suggestion that perhaps this might explain why classical music audiences are shrinking and no-one seems to want to read record reviews that are more than 300 words long and why television seems to get more brainless every time I inadvertently catch a glimpse of it.
Just a thought. And yes, the title is meant to allude to the essay by Jonathan Swift.
Let's listen to what was one of the most popular entertainments in the 19th century, an opera by Rossini who was able to retire, wealthy, when he was thirty-seven years old--from the composition of operas which were the blockbuster hits of their day. Here is the most famous aria from his most famous opera, The Barber of Seville: