This should help a bit...
I dont know about books...
Yes, read those, they are find for getting to know how to use (superficially) the richfaces control, but they are of no help if what one wants is understande how they work, modify or extend them.
In the Seam forum Adrian Mitev posted about this book "Practical/Using RichFaces" by Max Katz.
For what I can read in Max Katz blog, seems to be oriented to teach how to use the controls, and not to how to understand how they work, modify or extend them... but I might be wrong...
Anyone here can provide more information?