I never liked the notion that ancient aliens helped our ancestors in building Stonehenge or the Pyramids because I perceived a bias in the authors making that claim. I feel they assumed that ancient civilizations were less advanced, and were less capable of building these structures. I equate this belief with the same belief that led authors in the 19th century to assume that the mounds in Ohio were built by a civilization of white men because clearly the Native Americans weren't capable of performing this feat as they were 'savages' and lacked the intellectual capability of the Caucasian man.
It's somewhat insulting to suggest that we had help in developing our technology from outside sources, I for one think human beings are completely capable of that on our own...we're pretty remarkable in many ways.
If ETs are like Stephen Hawking describes, as a super predator species scouting systems for resources, I think our solar system may be seen as a poor choice. Though Earth is rich in resources for us, would it be rich enough for these ETs? I am dubious. The other bodies in our system that I have seen as being rich in a resource are our Moon (Helium 3), Titan (Hydrocarbons), and one of the outer gas giants (diamonds). These resources could be valuable for a Type 1 civilization, but for a Type II or Type III civilization? I am again dubious.
I don't think the smartest man in the world really thought this through, resources should be plentiful for a scavenger species, I don't see why'd they'd seek out intelligent life.