The musical of A Tree Grows in Brooklyn has gorgeous songs... I'd recommend the cast recording highly. The show itself doesn't quite come off... it's both a little too influenced by Carousel, and throws a lot of material to the secondary character of Cissy, who was played by star Shirley Booth, at the expense of the central couple. (It's kind of the same situation with Take Me Along, where Jackie Gleason's Uncle Sid has probably too much material, but the author(s) were writing for a star in the role and had to give an audience what they wanted). Still, "Make the Man Love Me," "I'll Buy You A Star," "Growing Pains," "If You Haven't Got a Sweetheart" and all of those terrific comedy songs for Booth, including the hilarious "He Had Refinement" and charming "Love Is The Reason" are all terrific.
As far as a book that would make a terrific musical...I've always wondered how Kingley Amis's "Lucky Jim" would fare. The central character's flights of fancy have potential for very inventive musical sequences.
"Gif me the cobra jool!"