It's worse than you think. Of those ~3000 users, some have already gotten their questions answered. That's not to say they won't be back, but I doubt that even half that many come to the board regularly. I.e. creating a topic advertising your book might be noticed by less than 1000 users.
However, I would be happy to add a link to any books you create in the pinned "Troubleshooting and Learning Center" topic, so as new users sign on and look for help, they are likely to find it.
So it is a bit of a gamble. Remember that CHIP is still in "pre-order" mode and won't be "GA" until around the end of the year. I think one could imagine an uptick in new BBS members around that time.
So, is CHIP so easy to use that people don't need to ask questions? No, I think that many more than 3000 people have visited the BBS and didn't bother creating an account because they were able to search their answers. There are plenty of sites out there that I have not created accounts on because my questions have been asked and answered.
So as long as your book is well-indexed by google, I would imagine a lot of hits as time progresses.