The book has perhaps a half million copies. This kit had maybe 5,000 made, with most used so perhaps 10-20% remain intact.
The FOOM kits were distributed in much higher numbers but now are rare.
I'd say anything that was distributed one per shop twenty five years ago fits the criteria to be considered rare.
My rule of thumb is this- Can I walk into a major show and buy twenty, regardless of money. If so, a book isn't rare.
If I put out a $10,000 bounty on this, will hundreds pop up? If not, it's rare.
Does rarity effect price? Somewhat, but not nearly as much as demand.
Something can be very rare, but not in demand.
This is a good example. I doubt more than a couple hundred of these survived, but the demand probably doesn't exist.