I have not read this book, but I did spend some time a few years back looking into the question because, like you, I found it interesting. I just didn’t find anything to cause me to think Shakespeare did not write his own material. It has seemed to me from the beginning of my search that the reason behind this speculation is sheer elitism. If I currently had the time, I would read this book, but alas, I don’t. Maybe some day I will. I like this time period.