I receive these absolute rubbish notifications. Not in email, but in YouTube.
I only really want notifications where people have replied to me.
Here are the settings I have ticked/unticked:
https://plus.google.com/u/0/settings
So I see no reason why I am getting notified of all this nonsense. These people aren't addressing me directly or sharing content with me directly.
Best Answer
As of writing, I think there's no option to change it, and the best thing to do is just to ignore it. You can tighten the notifications such that you get an email then you can know somebody replied to you (which you already have). But you can't tighten the notifications that appear in that window. So just ignore it, don't read all the junk there.
If you get an email and it links you there then fine, you could reply to that comment (if you see it within the junk in that window).