If you are going to buy Wallace Wattles, you may as well get this three books in one anthology. It is only slightly extra.
It's an easy read, and it's highly useful. You can get rich by acting in a certain way, and having certain beliefs. I believe this already. The one concept that was new to to me the importance of gratitude, which activates the higher vibrations of your mind, and assists mightily in manifesting what you desire. I also loved reading about rising above the competitive plane.
Currently, I am reading the science of being great. It is a very simple straightforward book that anyone can follow.
Is this the foremost book on Law of Attraction? No. Yet it is still worth a read, and highly recommended. Other books that I highly recommend in area of interest are The The Secret of the Ages
by Robert Collier, and Law of Attraction: The Science of Attracting More of What You Want and Less of What You Don't.
I hope this was helpful to you.