Really, you think Signs sucks? I wholly disagree, but that's another subject really.
As for the theory, you could be right. It's interesting how people can build these sorts of grand theories that, like you say, may have nothing to do with reality. If you want to see the ultimate example of this, watch Room 237 if you haven't already.
But then again, on the other hand, I think the dude makes a lot of interesting points and Shyamalan's work has always tended to have a religious tinge to it so it wouldn't shock me to learn that there's some actual truth here.