My list of things that could be only in one room:
Neather - Don't ask me. It's some kind of strange twist in the story
Crumby walls - You can use secret walls to hide things. These will be less important
Scrolls - If you can script, where do you need these? (Except some things that sound stupid when they're said by someone or so... (for example Architect's notes)
Spiders - Dev team didn't want to be so cheap again. (But after all the spiders aren't like they used to be so they might be using them more than that)
Tar Babies - They're just like roaches, why use these when you have roaches? (Ok, they fit better in tar mother rooms)
Yes, it has to be some of those. (My guesses in that order, from top to bottom)