What is the significance of having the made-up Terrance Mann in the film, Field of Dreams, as opposed to J.D. Salinger as the reclusive writer that is in the book?
I think that the very idea of Salinger appearing in film would have caused a litigious nightmare that the producers would have not wanted for the film. I think that Salinger was so protective of his privacy that to be included in film and in such a public way would have been a vision of nightmarish proportions for the producers. They must have understood this. Salinger threatened legal action through his lawyers against Kinsella in the publication of Shoeless Joe. He backed off of this claim because of financial reasons. However, one also would have had to figure that the mercurial Salinger saw something in the last name of the author as being mentioned in one of his own writings decades before. He relented on this end to be a character in the book, but instructed his lawyers to specifically prevent his likeness from being present in a film of the book. The filmmakers understood this, reason being why Terrence Mann represents every bit of Salinger in the film. The book's depiction of Salinger is a bit gentler, but the desire for reclusivity is all there as well as the disenchantment that he feels about the results of his writing. Terrance Mann is also perfect because he is of a different race than Salinger, helping to enhance both the differences as well as the similarity to him. Salinger probably did more to enhance his publicity by demanding not to be in the film, as nearly everyone watching understood who was being portrayed. To this end, it is significant that Mann is in the movie and not Salinger himself.