Somehow this popped up in my list - and I realized I never responded to it:
Yes, now this is possible via the software elk-herd: It can download a project, show you all the patterns, and the sample and sound pools… and it will let you find, and delete if you want, the unused sample and sound pool items.
Details here: Elk-herd 3.0 beta: Project Import at last!
I’m still waiting for +Drive APIs so I can find all the unused samples and sounds across all projects on the +Drive… but for now this will help you clean up individual projects so that you have space in the limited 127 entry sample and sound pools.