One thing that does not get considered very often
That the aliens may have a sense of humor and get a particular kick out
of messing with the limited and gullible inhabitants of Sol 3.
Coming many light years just to make strange patterns in corn fields
might be their idea of a great practical joke.
We assume both benevolence and warlike attitudes from aliens, so why
not a sense of humor, too? To find reality amusing is a true sign of
intelligence in my book.
Now of course the crop circles are someone's idea of a joke from THIS
planet, but how hard would it be for even a moderately superior alien
species to pull one over on the talking monkeys with car keys even today?