G+ attempts to solve a problem that has already been solved. The solution to maintaining different "circles" evolved into having different accounts. This was hindered for a short time by a lack of cross-posting but that was quickly solved by a set of APIs and app makers like TweetDeck. Personally, I have my family and majority of friends on FB, core friends and more comedy-driven people on twitter. I know I can crack certain snarky jokes on twitter that would offend my 2nd cousins and a high school friend. Those are the only 2 circles I need right now but if I need more, I can make a separate account. As it is, I cross-post my status updates, tweet snarky comments, facebook post family-friendly stuff, and on rare occasion G+ post techy things that weren't snarky. That results in about one post a month to G+ and daily posts to the others. I get the feeling this is a similar setup to many users of social media.
If our social lives are in either one circle or on an app which manages our circles, we have no need of G+. Communities don't move overnight. They shrink over time as their members slowly move from one pasture to a slightly greener one. G+ may be slightly greener but if travel there is difficult and I don't know anyone there, every time I head home for a "friend fix" I'm going to be tempted to never return. G+ needs to build a highway soon. Implement Twitter and FB accounts as "external circles" using the existing APIs. Let me make G+ my home while still talking to my existing circles. Let the external circles dwindle as everyone except our parents slowly move over to G+ but let us still talk to our parents. Until that happens, G+, your community will stagnate.