I had been using AE for about 10 years before I bought the AE Illusionist last year and I found it very handy and keep it nearby as a reference. Everyone gets used to a certain effects and patterns and his book exposes you to things you might not know were there. Doing tutorials will familiarize you with the effects you need to complete the tutorials, this will help you learn the ones you might only need once every other year, but you'll be glad you know them.
As far as learning advanced work, the book really doesn't go into complex stuff, just enough for most of the effects to get a basic understanding of what the effect does. I would give it a pretty strong recommendation for someone in the first few years of learning AE, and and for advanced users it's a nice reference to have around.
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.