If your site is set up properly you dont really need to spend any time on them at all.
I dont see social media as a prospecting tool. I see it as an SEO tool.
Set up your site to push out any new posts or pages to your G+/FB/TW accounts. All you have to do is keep publishing new articles like you already are doing.
Sure, occasionally someone will find your page click on a post and be directed to your site.... but more importantly googlebots will find your posts and index them as quality links to your site.... which will boost your SEO and keep your site/pages relevant in google.
I also know a guy who pays a highschool kid to spend a few hours per week posting links and blurbs about new articles/featured products/etc on social media. He also builds up the followers/etc for him by reaching out to people on it. He claims that kid is the highest ROI he has ever had on marketing dollars.
Maybe I will go down that road someday, but for now it is all just for SEO purposes. Personally I hate social media, it annoys me.
Will your friend share the kid?