One could also interpret the Great Silence as an extremely optimistic sign, rather than a pessimistic one: Intelligent species may be common, but as a rule they completely take over their galaxies (and anything else they can get their hands on), exploiting the resources so thoroughly that they crowd out any other species that might have evolved independently. So any intelligent species will tend to be the only one in its part of the universe, and the first to develop. If it hadn't been the first, its star, metals, etc. would have been converted to another species' ends and it would never have arisen.