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Umbran - I did say, one would need to spend a couple months (at least) developing your G+ members before an announcement of a product release for a new publisher. I wouldn't expect a new publisher to generate sales from a first post ever on either G+ or FB. If you're an unknown factor, you'll remain an unknown factor for a while anyway, no matter which social media you are trying to work with. If you have 6 months to develop your membership and recognition in various G+ communities before product release, all the better. If you have more than 6 months, then I recommend starting a blog on your project, that way you can develop your own sites members, rather than creating G+ members for Google.
Despite being a new G+ user, when I first started using it for my last project, on several industry related sites: here, the Paizo boards, the Cartographers' Guild and several others I am an active forum user since 2007, so I'm not completely unknown, I already had somewhat of a fan base of my cartography prior to the start of my Kickstarter. I have also done map commissions for a number of RPG publishers, including Paizo which adds to my reputation.
I don't know what kind of KS or G+ results would have been if I were a complete unknown, no doubt the results of marketing would have been worse off. So I cannot guarantee a new publisher is going to have success with G+ versus other means of cheap advertising, I just know it worked for me. And though I'm known, I'm no superstar, so I have to think G+ did help my marketing efforts a lot.
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Morrus - as far as converting to hard customers, since my G+ community's original purpose was to introduce, update and convert G+ fans to Kickstarter contributors, I did have the hard conversion as part of the strategy. While many KS backers were actually KS members who support many RPG projects, many of those were G+ users. I know when I made a plea that the final hours for my KS was coming due and I still had some stretch goals to achieve - shortly after I posted on my G+ page, I had a flood of KS contributors. It could have been coincidence, but it seemed like a reaction to my posting of it. (I got $6K in the last hour of the KS).
Interestingly, there are several general RPG map communities on G+ that aren't specific to the work of one cartographer (that I am a member of) and was in existence for months before I started my G+ community, whereas my G+ site focuses only on my work alone. Yet, I have a larger member base than those other G+ sites by a factor of four or five (though some are indeed popular with far more than my page). Its the maps I create that bring me members and customers, it surely isn't my cheerful personality!