Did you notice that in the '60s and '70s, there was a tendency for shows to change the arrangements of their theme songs to fit in with changing musical trends? And that this usually made the theme songs worse, not better?
Take The Patty Duke Show. The theme song is one of the most famous of the entire "song with lyrics that explain the whole premise" genre. The music is by Sid Ramin, who was a bandleader as well as the orchestrator for Broadway shows like West Side Story and Gypsy, and the first season's arrangement stuck to Ramin's big-band sound:
But then they rearranged the song to make it sound a little hipper and with a little bit more of a '60s beat -- and I don't think it fits as well; the music and the song are just too square (in a good way) for an orchestral backup that sounds like it was brought over from Batman.
And then there's The Bob Newhart Show. I like Lorenzo and Henrietta's original theme, from the first three seasons, much better than the disco-ish version they used for the last three seasons:
Are there any shows you can think of where they re-arranged the theme to make it sound more contemporary, and it actually worked better?