I don't really think of Graham Hancock as being a very good scientific source, but I think his ideas are a fantastic source of wonder about human history. It's simply fun to imagine advanced ancient civilizations.
Exactly. For me it's kind of like using wikipedia for grade school homework: the point isn't to use the article as your source, the point is to reference the wikipedia article's references. And I agree with your latter point as well: I don't really care whether his ideas about ancient pre-history are true or not, I just think they're really fun to think about. I love reading mythology even if I don't believe it, and Hancock's mythology is no different.