There are many soap-related books that a die-hard fan would enjoy, I believe, even if they did not watch daytime TV way back when.
Some examples:
Reference books like The Wonderful World of TV Soap Operas by Robert LaGuardia, From Ma Perkins to Mary Hartman by Robert LGuardia, The Love of Their Lives by Lynne Rogers, The Complete Soap Opera Book by Madeleine Edmondson and David Rounds, The Soap Opera Encyclopedia by Christopher Schemering, The Encyclopedia of Daytime TV by Wesley Hyatt, The Guiding Light: A 50th Anniversary Celebration by Christopher Schemering, etc.
Novelizations like The Guiding Light by Dr. John Ruthledge (published in 1937, but still findable on eBay and amazon), the Dark Shadows book by Marilyn Ross, etc.
Autobiographies like One Life by Ellen Holly (Carla on One Life to Live), Both of Me by Mary Stuart (Jo on Search for Tomorrow and Aunt Meta on The Guiding Light), Portrait of a Soap Star; The Emily McLaughlin Story (written by the late General Hospital actress' daughter, Mary Ann Anderson), etc.
These books focus on soaps and stars from the golden era of daytime TV, and favorites are bold-faced.
There are many more, but...this is a good start.