Is it worth putting the Roberts (and the Lackey?) books in a bag as if they are ready to go, putting them somewhere, and then putting a reminder in your calendar of choice that if you haven't looked at them in [time period] you get rid of them? If, in that time period, you decide that they are important to keep, you need to find shelf space for them.

Another question -- do you have something that needs the shelf space that you would rather keep? Or can you find something else that takes up that much shelf space that you would rather get rid of than those specific books?