No one is missing out on anything important. Mostly noise. For folks with my same mindset, I do believe I've cracked the code on most social networks, as far as what makes them worthwhile at all.
Twitter- it's the police scanners. Find them for your city, it's really the best way to know what's going on around you. Better than the papers, which can't report on everything or hide stuff for business's financial interests.
Instagram- is pretty much only useful for models, whatever sort you prefer. If you like models and it brightens your day to see a beautiful woman, as it does for me, it gives Instagram a purpose other than the noise it shares with most social networks. If it makes you happy and smile, it's a good thing. No, I'm not into pornography or anything risque. Though if I were, that would probably be ok, I simply value keeping a little imagination and mystery in my life and don't watch it. Nor are the models that I follow doing it as far as I know, but that's their decision. They mostly survive off product placement and payment for additional photos. Nothing wrong with innocent modeling, just like the olden days of pin-up girls and I hope more people support them in their endeavors.
Facebook- this one is better understood by most people, hence the popularity, but it's definitely the whitepages aspect of it. I use the instant messaging more than anything, as it's difficult to have an index of your old friend's emails until you're in touch with them again. Also, people just don't keep up on emails and maintain inbox zero very well.
Youtube- this, other than RSS feeds (through Firefox's Livemarks extension) is my main source of information. I'm not into cat videos, but I certainly love learning about astrophysics and other topics from Youtubers that are more knowledgeable than I am.