Another flaw is discounting Legacy Technology, which is something the famous Drake equation doesn't account for.
Have you read Rendezvous with Rama?
An ancient ship, abandoned for no one knows how long, stumbles into our solar system....
I agree with Arthur C. Clarke; I suspect our first contact scenario will be with a robotic probe of some kind. So, whilst we think of SETI scanning distant worlds/stars for signal origin, its not beyond reason that the signal will come from something that's moving. Hopefully, closer.
Biting the hand that feeds IT
