Just curious why you chose Lyx and not Org, for example. I still have your "emacs mini manual" open in my browser all the time, so I'm sure you feel natural in org-mode too.
I used Lyx because it enabled me to focus on the content without all the markup text. Writing Latex in Emacs can reduce the distraction, but not enough. I just wanted to focus on the content at the time. Learning Latex is difficult enough, learning how to use the major mode at the same time doubles the difficulty.
Obviously, I still use Emacs daily for writing code and other things. Just not for writing book.