The Prestige was a feud movie that had magic as the setting. Kind of like the difference between card magic, and magic that happens to use cards. This is a movie that happens to have magic in it. Unlike The Illusionist - which is a magic movie. The whole second half of the movie one long magic trick. The Illusionist, however, did around 87 million in the box office.
Now You See Me is a heist movie with magic in it.
Cast Away was a story about survival against the odds - the volleyball thing was just quirky.
A movie about Vernon could definitely do well - a movie about anyone could do well, and he was an interesting character in life. The trouble would be getting someone to care enough to put the effort into making it that good. Also, my guess is that if they did make a successful movie about his life, magicians won't like it on average.