While I can see what you are saying about mistakes in your drawings, they are still very good. I definitely think you should use the book in some way. After all, art supplies aren't just for sitting around.
I like David's idea. Take this one out once in a while and add a sketch or two, kind of a snapshot of where you are as an artist as you progress. It may take a few years to actually fill it up, but that's ok, it's sat this long. You might even stick to the realistic colored pencil drawings as the bench mark, since that is the theme you started with.