Whenever I watch a video or read a book from mainstream culture, I make it a point to see if any aspect of the story or presentation reminds me of something spiritual. I notice that wherever there's enthusiasm over a work of fiction, there must be a spiritual component that is activating the excitement and giving it life (however short-lived that life may be).
I've only seen the first two Harry Potter movies and read the second book. Anyway, for example, the stark contrast between Harry's life with the Dursleys and his home at Hogwarts reminds me of the difference between people ("muggles") who willfully scorn any mention of spirituality and those (wizards like Harry) who have a natural attraction or aptitude for living life among subtler energies.
A few years back in India, didn't a TV adaptation of the Ramayana cause somewhat of a stir? For a long time, I've been interested in the processes by which religious or spiritual themes cross over into popular media. In recent years, fiction based on Biblical (especially apocalyptic) themes have been pretty popular in America.
In my opinion, if Srila Prabhupada's books have real spiritual value, then they have potential to become very popular fictional adaptations. The impact of good fiction is basically the product of the author's heart, and if (as I believe) the attraction of "worldly" themes in popular culture is a grosser manifestation of spiritual longing, then the pure longing of real spiritual teachings would not fail to touch many people's hearts if adapted into a well-written work of fiction.
If a devotee's heart is full of God, and if it's God's will for the devotee to write a novel or screenplay, then that movie or a novel has the potential to be as authoritative as a traditional scripture. After all, today's novels and movies owe much of their appeal to the traditional storytelling modes from which they were descended. And those ancient storytelling modes were effective vehicles for communicating spiritual teachings.
I think a big reason why fiction like Harry Potter is more popular than spiritual teachings is because most people generally don't like feeling as if they're being taught anything. In that sense, fiction has a way of communicating to people by flying under the radar.
It seems like effectively adapting spirituality into the medium of fiction is not really an easy thing to do. If you want to sell a scary story about the wrath of God at the end of the world like some conservative Christian writers are doing, then that's not nearly so difficult as accurately mythologizing spiritual values such as love for God and single-minded devotion.
But it's not unheard of. There are the many short spiritual parables that we all know. And The Little Prince by Antoine de Saint-Exupery is a rare example of a popular book that is deeply spiritual and has a lot to say about devotion and purity of heart. But it's really hard to think of a full-length popular novel or movie that really succeeds as a true spiritual teaching.