I'm definitely not talking plagarism here. I don't understand why anyone would want to do that. The whole joy of writing is creating something that is unique to you/by you. I am referring to being inspired by a type of writing or the way a character is developed that can help you as you create your own stories and characters. You literally see how it is done and then get on with applying what you learn to your creations.
Non-fiction can inspire ideas as to how you get your own fictional world to operate to name one example. And reading across the age ranges is a good idea too. You get a "feel" for literature outside of what you do and I'm certain this will strengthen your own work.
My latest Chandler's Ford Today posts feature a two part interview with YA author, Richard Hardie, whose Temporal Detective Agency books, Leap of Faith and Trouble with Swords, are taking off in the South of England especially. I don't write for YA but the freshness of adventure tales such as these books helps encourage to keep my writing fresh, which can only be a good thing.
And all writing owes its foundation to a love of books encouraged in children at an early age (in my case, I really do owe my love of stories to my late mother) so wanting children's literature to do well is kind of self interest in a way. Without that foundation, there is no market for fiction for adults. And writers of adult fiction, I think, would do well to remember that.