I think that improving your analysis and visualization skills is very important. I posted a question on this topic recently as well (How can one improve their over-the-board analysis skills?).
But your question is more specific and I think you need to NOT try and study the Reassess Your Chess book in your head. The material he covers is too complex to be followed mentally for a class player. Also, because your visualization skills are not well developed you are going to waste far too much time and energy on firming up the image of the board and not be able to dedicate enough of your mental CPU to actually digesting the ideas in the book.
Notice that I use the Chess Success book in my visualization training. McDonald's book has diagrams every 5 to 8 moves and his analysis is very direct with shallow trees. It's really a great tool for doing visualization training. And even though I am fully able to follow the moves in this book and accurately draw the images I still go over each game with his analysis using a board after I do my training so that I am certain I have understood everything he has said.
You need to separate the idea of study and training. When you are studying a book like Silman's or Pachman's you need a physical chess board and a computer board as well to get the full benefit. Those types of books are for study. Use something simpler for visualization training.
Here is some advice from USCF Life Master A.J. Goldsby on how to study a chess book (from his Training Program page).
Many people think studying a chess book can be done by reading and
occasionally looking at the diagrams. Nothing could be further from
The only correct way to study a chess book requires AT LEAST one
chess set. And a good little analysis set on the side. Maybe a
magnetic set to boot.
Basically, to really get any real instruction from ANY chess book, you
must set up the position and play through the example. (More than
once.) NEVER (!) (Even if you can play blindfold chess like me!!);
think you can follow a series of moves in your head. Set up your board
and play through every example and every single variation!
When I study, I often set up a chess board on my table. I have a
little peg set off to one side, that I keep the current position on.
And I also usually utilize one magnetic set. I play over every single
move, line and variation. Often I will question a line, and spend a
lot of time analyzing lines the author may not have even looked at.
(As a Master, I have an obligation to try to find as many mistakes in
analysis as I can. And on top of all this, if it is a very complicated
game, I more often than not will have the position set up on at least
one chess computer, analyzing the game and the variations.)
Even though we live in a very digital age I think it is important to use a real board as well as to keep another board with the current position so that you can quickly go back to the original position and consider it at the same time as you are looking at another position for analysis on your main board.