Among people who really love books this is so common. I've seen some really cool book art, but there is that fear that you are messing it up. on the art journal board someone suggested starting with a book that you aren't attatched to, or a foreign language book that you can look at as a pattern.
I need to convince myself that it's ok to use book pages in project.I know what you mean - i only use looks that are already unreadable, but i still had to take a few deep breaths before i launched into my first project with them!
when the cover actually fell off, i altered a copy of socerers stone into bookmarks. my daughter was shocked to see me cutting it up. she said books should be repaired. but then of course she wanted the bookmark when it was finished. .....photo is from a previous semester.