With Google+ and other social sharing (Twitter and Facebook) increasingly becoming a significant search ranking factor sharing comments on your blog posts using the Google+ comment system sound like a good plan.
FAQs about the Google comment system https://support.google.com/blogger/answer/3007761?hl=en
What about spam?  Well like most things Google, don’t worry about it, they filter most of the spam comments for you or let you know it looks like spam or someone in the Google+ community will probably report it for you.  So you still need to be vigilant about spam comments  especially if you get a lot of comments or have a large Google+ following but largely spam is taken care of.
The most reliable looking Google+ comment system for WordPress seems to be ‘Comments Evolved’ formerly Google+ comments here http://wordpress.org/plugins/gplus-comments/