Right. I am totally new to this.
So I see the benefits, except for the fact that the Evernote API doesn't have access to Spaces. I have confirmed this in two ways: (a) I tried it myself - if a notebook is shared with me, the notebooks in the Space are inaccessible through the API, and (b) I got confirmation from Evernote dev support on this matter.
So for me, the API thing is a deal-breaker. I will need to use shared notebooks to interface Evernote with external systems.