Call me careful, paranoid or whatever but when G says they don't like social media spam and could penalize me for it, I'd like to know what it is so I can stay away from it.
You are showing your youth.
This is the game we have always played with Google (and every search engine that has come before it or *kinda* after it). Your quandary is as old as SEO (and now other related services).
The FUD surrounding this game has always been enough to keep me on the straight and narrow
Then G has accomplished its goal.
even when I probably would have been rewarded for it
Yeah, ask those affected by Penguin how that worked out. That worked for a really long time. Until it didn't.
This is not just websites. This is life. There are lots and lots of brick and mortar things that will get you rich in the short term. A cheat here, a blind eye turned there. Some people neck deep in it get away with it and never get caught. While others pay terrible consequences. And still others who only edged around those things get nailed to a wall for it.
Google is no different than your friendly neighborhood government or god. They aren't going to tell you the hard line on the rules because if they do, the @$$holes of the world will exploit it for all it's worth.
This is the very basis for business ethics. How far do you want to push the rules to make a buck?
I personally don't anymore. And really, it is because I kinda suck at pushing the boundaries. I just don't have the stomach or the balls to do it well. My end game these days is if what I did makes me proud, I did good.
If you are trying to make G happy, you have to realize that you are serving a fickle god. If that is your goal, follow the rules to the best of your interpretation. But you cannot expect any more than that from G.