I have just updated my review calculations to better reflect the actual usefulness of the books. Final value before price now consists of 50% meat or cheese depending on the book’s focus, 15% of the other ingredient, 20% sauce and 15% generic nutritional substance. This led to slightly higher values across the board for all existing reviews, but nothing extraordinary. I just wanted to avoid situations where a book is dragged down by too little rules or flavour, when there’s nothing to justify that.
I might use a combined category in the future if something presents itself. The upcoming GURPS Discworld looks like a likely candidate.