It's funny you should mention those compilations, because… not only am I familiar with them, but in fact I was the person who designed the packaging for the Level 9 Compilation! (Check the small-text credits on the back of the box – I got a nice commendation from Mike Austin for producing something that looked so authentic to the Level 9 style!) However, those adventures don't use Inform files; both sets use their own proprietary formats, and Stefan Bylund produced very nice Spectrum Next versions of the interpreters needed to run them. You're right that some of those games are indeed also available for the Spectrum +3 (either exclusively or with pictures exclusive to the +3), but they still use a special interpreter and aren't available as Inform files.
In my previous comment, I was thinking primarily of those few adventures for the Spectrum +3 that are ONLY available on the +3 (not other Spectrum models) on CP/M disks, and which could presumably be extracted from those disks and run 'natively' on some other Inform interpreter, such as ZXZVM on the Spectrum Next. Presumably the same would also be true of adventures packaged up as Ozmoo disks for other platforms, though I haven't investigating extracting those yet either. I don't suppose there are lots of adventures like this, because Inform-format adventures are mostly released as separate Inform files and don't need to be extracted from a platform-specific disk… but there may well be a few like that, so it's worth bearing in mind.