Vanities is based on the play of the same name which was a substantial off-Broadway hit in the 1970s. This is the play that pushed a little known young character actress named Kathy Bates to a brighter spotlight. I can't remember if she originated her role, but she did play it a while during the 4+ year run.
It has a cast of three women (no men, no chorus) who we first meet as high school senior cheerleaders in a Texas town (Think that they all say "haskell" instead of 'high school'.) At this point in their lives, the three are almost interchangeable.
About 5 years later the three have gone to college together and are getting ready to graduate. They have begun to think differently. Change is in the air.
After another 5 years or so there is a reunion in New York. They have gone on very different routes to get to this day.
Years pass and they meet and reconcile back in their hometown.
The script is very dated with specific 60s-70s references. It is also tight enough that the addition of songs does not reveal these characters further. Vanities does not cry out to be a musical. It is not a "bad" show per se, but so much is unnecessary in the musical.
Find the original script to the play and read it. (It is full of 3 women acting scenes.) You will find out that the last sequence, the one where they meet back in their hometown, does not exist in the play and was written to bring these women into the sort-of present day.
The play is much funnier than the musical because the songs slow the scene-arcs down.
On the other hand I am a firm believer in seeing everything. Said the great Moss Hart, "Nobody learns anything from a hit."
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher