That’s not driving the value of IH 181 now, though. The “reading” component of the hobby, such as it was, is baked into modern values. It’s valuable, because it’s been valuable. Nobody needs to buy the book to read it anymore, and everything gets slabbed.
There’s no real objective reason why 181 should be so much more valuable than 180 (“story” isn’t a sufficient explanation in this case. This isn’t the Death of Jean Gray, etc) other than it’s been that way historically and a lot of people in the hobby have a vested interest in that continuing.