I don't see how its such a bad theory. Consider the effects of an advanced civilisation coming into contact with a primitive tribe of humans. Unable to explain technology the way we can now, its not a huge stretch to imagine humans worshipping extraterrestrial beings, believing that they possess magic that is beyond us.
Its not an entirely apt example, but consider the Aztecs when they encountered the Spanish. They believed they were gods because they were like nothing they had ever encountered. The reason this isn't a perfect example is that the Aztec's already had an established religion prior to the Spaniards arrival, and they just applied the identities of their gods upon the newcomers.
It makes a fair bit of sense when you think about it. Is there sufficient evidence for or against it? No of course not, its just another theory. To me it seems stranger to simply assume thatearly civilisations imagined gods out of thin air. Yes they bear traits that exist in their surroundings, but most other mythological figures seem to have been based on something solid.
Unicorns - Some believe to be based on rhinocerous.
Dragons - Discovering the fossilised remains of dinosaurs.
Centaur - Seeing foreign riders, so skilled that they seem to be part of the horse.
Again these are theories, but they make as much sense as most other explanations.