This is an impressive write up. As I'm reading through I realized that you've become "top of mind" now for whenever I have a Google+ question. And I very rarely see anyone writing articles like these for Google+.
I thought number two was interesting. It is easier to build a bigger following on Google+, and I had not really thought about it from the SEO perspective.
@DaveGallant Thanks, Dave.
One of the reasons that I like G+ is because it's the engaging platform for me.
The more you share and participate, the more profile you have. If someone enjoys your posts, they can put you in a circle of "engagers" for example, then share that circle with their followers.
It was in this way that my follower count (number of people circling me) increased by nearly a thousand in a couple of days.
As far as SEO goes, number of +1's has the biggest weight. And as you know, they're everywhere (or soon will be).
Now, I have to look at Pinterest more. I think there is a way of using in with G+ because of the visual element.
Once again, thanks for the encouragement.