I can attest to the existance of multiple dimensions; I've had more than one experience with them. I spent several days in Lorne's homeworld of Pylea. I do think your have something to your theory. We had an experience with alternates in Sunnydale...an alternate version of Willow. Our Willow is human, but her alternate was a vampire. I think it's quite so that different realities can be a reflection of events that came out differently. However, as for why they would all be coming together in this way, I'm not certain.