Interesting. Lewis' "Mere Christianity" was the first step in my conversion to Christianity, a life changer, and I wouldn't claim "Atlas Shrugged" altered my life it was a strong influence in my thinking.
In some ways, Atlas Shrugged confirmed what I'd already believed about Capitalism, Government and Fascism (the marriage of Government and Business where only the well connected thrive economically.)
In other ways, Atlas Shrugged really opened my eyes towards the different types of people they are (the characters in the book) and the insidiousness of Communism and Socialism as political systems. I credit Atlas Shrugged for making me a much better critical thinker in that regard.