As with anything, I think there's a balance. Creating a character like Coulson was great and worked well, but he was still a rather minor character. Personally I like to think of the MCU as a completely separate verse, like Ultimates. while it uses the comics as source material, I hope it continues to do its own thing as well instead of following too closely. Some new backgrounds, new relationships; they have the opportunity, so why not use it? I don't think the films should really influence the books, though, unless they want to make another new universe to play in. Let the books be the books and the movies the movies, that way everybody wins.