One factor that could be worth considering is the concept of timeless wisdom. It's very easy to knock any religion but overlooked is the value to be found in some of the stories, sayings and so on. For example, someone once told me that most of the members here on the TWC are atheist, but everyone can appreciate the value of a quote such as:
"Let he who is without sin, cast the first stone". - Jesus, quoted in John 8:7, the Bible.
Jesus is making a point that since nobody is perfect and we all have made mistakes, we (as a society) shouldn't throw stones at each other, either literally or metaphorically. That's just one example; my point is that perhaps Holy books are valued not only because people believe they are holy, but also because they really do contain some valuable wisdom. I've read sections from the Quran, the Bible, the Sikh holy book the Guru Granth Sahib and the Buddhist teachings, and they all lead me to this same conclusion.