One of the ideas I had in mind is to have an in-game encyclopedia with full details on monsters, items, effects etc., where entries would open naturally as you play, but if you are interested in something particular, you'd be able to open them immediately with some purely symbolic amount of gems.
The gallery, however, will be the main target for spending the dream shards. I know I haven't updated it in a while, but there will be much more content to unlock, and not only images.
I'm also open to suggestions!