Back when Americans were literate, a lyrically clever jingle like this one would resonate with any high school graduate's funny bone ("singin'" rhyming with "picnicking in" and "exploring in" among others, each rhyme its own joke for its own sake).
The jingle writers and the listening audience were sharing a wink. Cynicism doesn't require intelligence, but understanding this commercial's appeal does.
The song, the arrangement and the singing are backdrops to give Dinah Shore, a world-renowned singer, an opportunity to sing during a driving adventure with three harmony singers in a Chevrolet, the product being advertised.
Excellent post and your observations are right on.
How many people today still understand what a "wink" is? It's a physical means of sharing a joke, a common understanding, a common culture.
You are absolutely right about the singing. We have become consumers rather than producers of music. When this commercial was made, people still bought sheet music and played and sang to it at home.