Paul, You are correct, I absolutely believe that "you can benefit from social media, no matter what business you're in" I'll read my post again, but I don't recall saying that "tweeting will yield new customers equally for a tattoo parlor and a funeral parlor." In the work I do, we don't take a cookie-cutter approach to the strategies we develop for our clients. We perform research and make educated decisions based upon the data we have. For example, I'd want to know if customers of a tattoo parlor are active on Twitter before I recommended that strategy. Maybe they are more active on Pinterest because tattoos are more visual.
Keep your eyes open for that study you're looking for. If it's not already out there, it will be soon.
Thanks for taking the time to read my post.