I was going to post the advice that you go, but I looked at the date of the OP and I'm thinking that this book signing may have already happened. If so, did you go?
Since this is a book signing and not English class (or a book club meeting), I wouldn't feel the need to have already read the book before going. Especially since this book is non-fiction (that's all I pretty much read anyway - I rarely read fiction these days).
Besides, it's a good way to get out of the house and be among people (and create a nice memory of meeting someone "significant").
I went to a spell of book signings many years ago - these signings are among the few times I've "rubbed elbows" with someone "famous". Here are a few I went to:
Christopher Darden ("In Contempt") - I had a big crush on Christopher around that time, which made me nervous about making eye contact. From out of the corner of my eye, way before it was my turn for him to sign my book - I think I saw him looking at me.
(I'll just remember things that way, lol.) When it was finally my turn, I was almost in a daze - I was speaking to Christopher Darden! I remember him smiling at me...I wish I had really made stronger eye-contact with him. That moment meant a lot to me, and maybe to him as well.
Robert Shapiro (whatever post-O.J. book he had out) - I didn't buy a copy of his book, but I went to a lecture/book-signing he held at a local bookstore. He's an ******* - I had my hand raised because I wanted to ask him a question (he was taking questions), and he didn't acknowledge me.
E. Lynn Harris ("Just as I Am", "And This Too Shall Pass", etc.) - very personable. Great writer, great personality.