Why not both?

Getting updated right now is quite a chore, so I support the idea of a notification tab. But a shares tab is worth as well. Right now, people don't want to resteem so as not to drown out their own content, which is perfectly understandable. So the good content doesn't meet new eyes because nobody cares more about someone else work than that of their own. But if they were separated, I for one would gladly resteem more quality content. But as it stands, me, along with others try to get our own stuff noticed.