Well, here is my two cents. I disagree with the idea. As Pavel said, you don't own anything, albeit the format is nice etc. There is so-o-o much knowledge stored here it would be a huge loss. Searched properly, that knowledge database can be a big help to newbies and save a lot of duplicate postings for easy to find solutions.
I'm with you on this Gordon. If you look at the Stats on the bottom of the home page, you will see a lot of guests here consistently throughout the day, which means people are using the KB established here to find answers. If you want Google+ simply to get people to sign up and experience a socialesque platform, I think that's misguided. This is business, serious business. Do you really want to loose all the great info already archived here? Moving to Google+ would be starting over with
0 info. Referencing info here would have people jumping through hoops to get answers and they will go elsewhere. It's human nature.
If it's ease of signing up using social media logins, take a look at Social Login
http://custom.simplemachines.org/mods/index.php?mod=3580 As far as I can tell it's compatible with this version of SMF and covers most of the common social media platforms.
As for what is here now, for problems such as Spam, SMF forums has lots of addons to address the issue(22 right now) AND a lot more. I use Stop Forum Spam and Bot Buster and both work relatively well. Run across a bad IP? Ban it from cPanel or use on of the many .htaccess files available that bounces the most common bots.
Want a Like button ala Facebook, got it. Want a section with a format like Facebook? Got it. If you can think of it, there is probably an addon for it at the SMF forum site
http://custom.simplemachines.org/Also, you may find that the opposite could be true, that people will shy away from Google+ since it represents Big Brother. And possibly get a bad reputation for Abantecart. Is it worth the risk?Running your own forum independent of "big business" embodies the Open Source philosophy and MHO is to keep what we have and make it better. I have run an SMF forum since 2004 so my experiences are yours.
Edit---> Parting thought, what would be returned for a search for
Abantecart Forum for a new user? Would it even show in Bing or Yahoo?
Also, it's 3:40 AM EDT and there are 121 Guests on the forum. I think people are using the KB here. Admin can see exactly where they are too, to get an idea of what the overall interest, problem, whatever is of the guests.