I would theorize that it would give a short term bump to sales by people who were pumped enough about the movie that it made. Want to know about the characters. Long term most of those customers won't keep up with the hobby, but some may stick around. I would imagine that legacy characters, rising costs of comic books, and general decline of interest (especially with the quality of a number of Marvel stories being questionable) leads to a lack of retaining casuals. Additionally it can be daunting to get into comics with such a wealth of history and books to choose from.
Again, just my theory. I'm ain't got time to compare sales numbers in the months preceding and following a movie release for titles that coincide with the movie.