As for having a mostly techie userbase it's just where it's market penetration starts, and techies are the most likely to adopt a new invite only app.
And that's also where it's market penetration ends. Non-techies don't want to deal with invite stuff, so they don't join Google+. Now the only people on Google+ are techies, and that's where it's going to stay until Google kills it off in a few months like they've done will most of their other recent projects like this.
Give me one good reason why non-techies would ever join a social networking site filled with techies when they already have Facebook that fulfills all their needs?