Thank you both very much, and sorry for the delay. "Subject" and "Classifications" are both able to bring up entire collections tagged this way (and we could productively use categories to distinguish our collection areas - I really like seeing that in use, Irene), however what is missing in these is the extra layer - independent descriptions of specific materials within a collection, directing researchers to one part of the collection, and with other faceted search terms. For example this describes one record within a collection, but there are ones that describe a great many:
I imagine it could be possible to make something similar as an artificial "collection" of guide entries, with related resource links, maybe with modifications to the display and search options, but it would be very hacky.