If one of these books were lying in an abandoned asylum, it'd be worth more than one of those old lovely radiators or a couple of oak doors and considerably less of a pain in the arse than removing lead off the roof!
It definitely seems like a fantastic book on this subject where there are few out there. Margaret Rutherford's has been a good resource as she produced one of those Shire books which provide a comprehensive summary on asylum design. Her 2003 three-volume paper on asylum design and landscaping is really good too, very in-depth but not from a purely architectural view. Most of the really detailed info I have found is in those sorts of research papers.
Any chance you could share a couple of images from the pages please? I'm interested to see just what the book looks like inside. Lots of technical drawings or photos, or mostly text or both?