When discussing this topic, I often feel dissapointed because the arguments usually go to extremes. On one hand, the defenders of the current paradigm use to laugh at these proposals and they ridicule the whole stuff without facing a serious debate. On the other hand, many people who support the ancient astronaut theories are absolutely convinced of their ideas without the slightest dose of criticism about their supposed "evidence". Sometimes, they seem to be a kind of religious believers, seeing aliens' traces everywhere in the remote past.
I think the Ancient Alien theory deserves a serious approach from other perspectives, recognizing that the conventional view about the "ancient gods" might be flawed in many aspects. In other words, there are several unexplored paths that do not match either Von Däniken's theories or the academic view on our Prehistory (or Ancient History). As many authors have pointed out, the existence of an advanced influence or culture in a distant epoch could be explained by other reasons, for example a human civilization with a higher state of conciousness or the presence of beings from another dimension (not from a far planet in a remote galaxy). This latter option was proposed by serious researchers as Jacques Vallée and it has been a valid theory to explain the whole UFO phenomena for years, although it's just a hypothesis that should be confirmed on solid evidence. Obviously, the problem arises when talking about things that do not admit experimentation in our five senses physical world.