Spoon full of sugar helps the medicine go down, as Julie Andrews once sang. That is what was revolutionary at the time about SS (other than the integrated races being the human stars, which was also pretty revolutionary for that time period).
You don't have to teach things 24 7.... after all, sometimes a good laugh is what kids need. Not to mention the fact the original idea was not only to make a show kids will watch, but a show thast their parents will watch as well.
But I feel that the most important lessons come from the most unlikely sources. Bert and Ernie arguing can be a great example of many things. Logic, the fact that friends can fight, difference of opinion, and various other things. the Song I Love Trash may not seem educational, but it shows that people can like different things that other people may actually hate. Plus it also shows that it's normal to have a prized possession, especially when your youngwer, to constantly carry around (same thing about the song and posession of Rubber Duckie).
It is indeed times when you aren't thinking that you tend to learn more.