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.
My Name Is Legion, I hope that my belief didn't led you to change your opinion on what is possible in space. I may have been wrong in the past on certain opinions, but I tend to throw things out there on the Internet to see how people respond. This is one of the ways I learn and grow. I am open to change and I am not locked in my opinions.
With scientists now speculating that there are a possibility of a large number of planets that are life-bearing, and some of these planets having come into existence earlier than our world, I think it's equally likely that there have been an x number of civilizations, and I think it's equally likely that y number of civilizations have developed FTL. I don't think we can judge the capability of other civilizations when even our own scientists acknowledge that we are a Type I civilization.
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.