I very rarely read celebrity endorsements, so I really don't know for sure. If there is an endorsement on the book cover or back, I generally think, "Oh, that person liked this book." It doesn't have anything to do with whether I will read it or not. If the endorsement comes from a writer whose works I enjoy, I may have a bit higher expectation for the book, but not always. I have seen endorsements on books that I didn't care for at all.
As for general popularity, it is really hard to say. Hype, reviews and endorsement seem to get book onto the front shelves where they get noticed. I don't know if that causes a great influx of readers. It is not bad to have the books be noticed, though there are many rather unnoticed books that are wonderful to read too.