Here is a tip that will hopefully adjust your view on Google+. If you are a business, you will be well used to the idea that you want to build a targeted email list, but can you do this on G+? Well, on the surface the answer is 'no' as you don't have access to many people's emails. Even if you do (i.e. they have their email accessible on their profile to 'you'), it may not be wise to just sent them 'a shot'.
Instead, you can look to use Google Circles and the technique below to start building up small niche lists.
And remember, these may not be HUGE lists but they are dedicated niche interest circles/lists to which you can also send an email.
The first step is to ask people if they would like to join a circle that you will then notify by email for those posts.
You can use several methods, including the polling method below. As you can see from this example, there are different 'lists' being built here for different content and with different promises e.g. I will send content daily, or a few times a week, on different subject areas.
You will find your own way, of course, but this should give you an idea...
Building the circles
You will need to 'gather up' the people who have opted in e.g. by hovering over and adding them to the new circle you are creating.
I find the optimal size is below 100 people as often the 'notify' option (see below) is not available on larger circles.
Tip: if you find the check box is not available on the circle size you've chosen then split the circles into 2 or 3 and try again.
There is more on this in the Q&A section of the PYB site.
Then it is time to notify
Once you've built the circle, and you've got your content ready, you can then 1. choose the circle, and 2) 'notify by email' (you know, that little box that is sometimes available to 'check' when you post).
When you've built a circle in this way, you will find a positive response when people receive the content in their inbox.
Very simple but a very effective way to get the messages you want to people who 'opt in' to wanting them. You will almost certainly find people will engage more with the content too.