I think the question isn't whether or not we are alone, but why don't we know the answer. As you said, it's 'wildly improbable that we are alone.' So the great question is, why is the universe so quiet?
Jill Tartar has talked about how we would need to think about investing in a powerful radio beacon for 60,000 years if we wanted other aliens to know about us. That gives one an ideal of the scale of time and distance SETI is dealing with, assuming their assumptions are more realistic than Fermi's was.
Like in a video game where new areas are rendered as you discover them....