Scattershot, I agree 1700% with your first reason. It takes energy to be around boring people!
I enjoy being by myself in order to synthesize information from outside myself, although it's always been my preference to be around other people without being directly involved in whatever they're doing. So although I like being left alone, I've never really been in love with being alone. When I'm alone, I'm either reading, writing/thinking (and I'm not using that word in the Junging functional sense, because it's more like a blend of thinking and intuition, heavy on the intuition), doing something mindless (like video games or certain homework), making contact with people via internet (facebook, forums, etc.), or ruing the fact that I'm alone. Even boring things like cleaning up or doing homework I'd MUCH rather do with someone else than by myself, except for the fact that sometimes I'm distracted by the other person and fail to get the stuff done.
So ultimately, I guess my answer would be a combination of 1 and 2. Otherwise, I'm ready to go find more people. I usually just do the weird stuff around other people, especially family and close friends. Occasionally not family or close friends, which tends to freak other people out, but whatever about that.