This was a fun read, but I don't buy it that highly intelligent aliens have been here before -- or that they are plentiful in the universe.
One big problem with cosmological modeling and star and planet counting is that the experts who do it -- who are very, very good at astronomy -- get two big things wrong. First, they know almost nothing about evolution. Something like 800 -900 million species have existed on planet earth (about 8.7 million are around right now). How many of them developed real technology and/or the scientific method? Just one -- and VERY recently. And it was an incredidible fluke. It is very likely that we haven't detected intelligent life out there because it either doeesn't eixst at all or is very, very rare. There is sinply no evolutionary push whatsoever toward highly complex or intelligent life.
The other big problem is that many of the things that make highly complex life possible are much rarer than most people realize. Astronomers surely know this but they seem to keep it a secret. For example, most star systems are binary (two star) systems. Binary systems are VERY unfriendly to life. As another example, very few stars are the right size to be friendly to life. The big ones burn up way before there is time for anything too complex too evolve. Many stars also emit the wrong wavelength of light. Not just any wavelength will do, by the way. Many stars that are otherwise very good candidates for complex life are too close to black holes, get hit too often by asteroids, or have highly eliptical orbits. The list of things that have to go right is a VERY long one indeed. Yes, probably long enough to make ET very, very, very rare, even in a universe as huge as ours.