Interesting post, though personally speaking I simply don't believe in the "ancient aliens" theories. I wrote a post explaining why a few months ago, but in a nutshell, I do think humans could have done all the things you mention. We humans often put ourselves down, and we're always looking for someone or something "out there", greater than ourselves, almost to take responsibility, to take the lead.
Also, we have a habit of trying to reconstruct the past in the image of the technologies and fashions of the current period. So a human-like figure depicted in the Nazca lines is seen as wearing a "space suit" – just like the one Neil Armstrong wore. An ancient Egyptian pictograph is interpreted as a "lightbulb" – but as the kind of lightbulb that would have been used in the 1970s and 80s, not the kind most people use today.
I do believe that much of history has been obscured, however I would like to think that in ancient times maybe humans had technologies that we don't even know about these days. I don't know why we lost that knowledge, but at some point, it was lost. That's my theory.