I don't honestly know how well it will work for you, if you think people would want it. But it's definitely going to perform way better than just a normal copy of the book that isn't signed. Anything that can be personal in that sense is super powerful. Something other people are doing in your situation that does work really well is to have a section side of the news letter. It's like a little extra thought, an extra tip, a link, a resource,. something really small that takes you hardly any time to put together and that you can unlock access to with one or two or three referals.