Fascinating stuff from a great communicator.
I'm not nearly as anti-SETI as most ufologists are - what's the harm in looking for radio signals? It's not like it costs that much money, and, as I said in a radio interview once, I think ufologists are just jealous that SETI has been more successful in engaging science and the public than ufology has.
But, whether you like Sagan or SETI or you don't, watching him do the calculations is interesting, especially if you accept the possibility that there may be millions of technological civilizations in the galaxy (a number that seems way too high to me; I would always go with a more conservative estimate, based on the principle that it's better to be pleasantly surprised than rudely awakened). It stands to reason, if that's the case, and if they manage to survive what Sagan calls their "adolescence", that they could - indeed, almost certainly would - develop the ability to travel between the stars, if not in person then at least in the form of advanced probes, probably using some form of artificial intelligence. From there it isn't a giant leap of logic to conclude that one or more of those probes, or perhaps even crews, made its way to Earth at some point, and took a look around. Perhaps they're still here. One can't prove that on the available evidence, but it's not an unreasonable hypothesis, even if there had never been a single UFO sighting.
Ironically, given that he was not a supporter of the ETH, Sagan's reasoning, using Drake's equation, should give comfort to those who are supporters of the ETH, and should give pause for thought to those who would dismiss the ETH out of hand.