Yes, that’s exactly what I’ve been doing. It’s helpful, but not that helpful. 
It is unfortunately a far cry from the kind of “pulling it all together” that I’d like, and that I think Fibery has some promise to allow.
Well, more or less, yes, sort of, mostly. Any fields that had the same/common data would be shared, yes. E.g. Name, Email, etc. If necessary you might have to do a little jiggery pokery to make e.g. a system that uses a single “name” field compatible with one that uses first/last names (separate fields). And you might need to set one source as “canonical”, where the rest can’t write to it and only use it for matching, or just don’t write to it at all. But really the point is a field-level data sync, I think…
Mm, that’s a good point and, to my surprise, raises the already-rejected idea of field-level permissions, e.g. Customize Fields via Rules. Hmm.
So I don’t know. But the promise of it seems, to me, to make the challenges of it worth thinking seriously about, and potentially solving. If Fibery wants to truly become the unifier of data, and thus the central “sense maker”, the place where all data comes to become “sensible” and derive insight from (as seems to be Fibery’s overall ambition), then I think this will have to be a part of it to truly achieve that.