I've read Siddharta and yes, in a way it changed my views. I don't know if calling it "religious" views, or just philosophical, however. Another book by Hermann Hesse that had an impact on me was Demian.
Anyway, to me, the message that I got out of it was mostly about the importance of stories. Because that is what both versions of the events that Pi told the author are. STORIES. Stories are our ways of fantasy/escape to deal with terrible events that happen in our lives.
Which is why it would make sense that the Bible is the greatest selling storybook of all time. Because the earliest(and greatest) stories of mankind, the cavemen paintings in caves are a little too bulky to be sold in your local bookstore.
Anyway, to me, it is about the power of stories and their "magical" ability to help us cope with life.
However, I will admit that I think I might have been a little biased towards to the movie to start out with because I know Ang Lee is a great director, but I just couldn't really "get" a lot of his earlier arty movies(in part becasue he made mostly Madarin films at the start of his career and despite being a Chinese myself, my Mandarin is terrible. I know there's such a thing as subtitles, but something always gets lost in translation.). Brokeback Moutain was a nice one from him, which I throughly enjoyed, and NOT just because of the gay sex. Face it, if that's ALL I was after, I could just surf porn.
Haven't read Sidhartha or seen the movie of The Life of Pi, but I did read the book when it came out and loved it. However, I didn't really see it as a religious book. Pi is sort of a non-denominational religious person, but I don't believe his religion was really what he was talking about there. Hopefully not to spoil anything for those who haven't read it or seen the movie, but The Life of Pi struck me as more of an exploration of personality and a "man vs. himself" narrative than a story that posed religious questions. Granted, it's been a couple years since I read it, so I'm going on memory here, but it seemed more like Pi was questioning himself than his beliefs.
I also felt like there was a certain irony to the book's story basically being dependent upon the reader's belief in what really happened--like the tentative beliefs of an agnostic--and that's what makes it unique. Faith can be great, but maybe it doesn't produce the best stories all the time. Sometimes uncertainty does.
I've read Life of Pi, but not Siddhartha (yet). Siddhartha just doesn't seem like something you read casually on the train, which is where I do most of my reading.
Anyway... I liked Life of Pi, insofar as it was an interesting piece of metafiction. However, if read as a literal critique of agnosticism it seems like a poor argument, since individual agnostics have their own narratives about life and its weightier issues, and the idea that their stories aren't as good as religious narratives is a matter of opinion. I was also disappointed that in spite of the main character being Hindu (and Christian, and Muslim) that Hinduism really didn't get discussed the way the other religions did. Did Life of Pi change the way I thought about religion? No, probably not. If anything it was sort of an affirmation of the idea that we live by stories, and they in turn both form and reflect our experiences. I liked the book, but felt like the author handled the themes of religion & faith in it in a way that was a bit too heavy-handed. I wanted to feel like the rants about religion were Pi's rants, not Yann Martel's.