@Zacs
//The size of the universe means that the possibility of the 'miracle' conditions for life being repeated are multiplied, surely?//
Hmmm… tricky.
Multiplying up also works for killer asteroids, gamma-ray burst stars being too close and all the other disaster scenarios which threaten whatever life did evolve in the remoteness of space. ALL probabilities play out, not just the goldilocks ones.
The Drake equation does factor in a probability of life not lasting long enough for the emergence of intelligence but I think his work may have pre-dated the discovery of gamma-ray bursters and other exotic items.
Anyway, emergence of life is one set of probabilities, emergence of intelligent life a separate thing. Drake even added a factor after that, accounting for the window of opportunity for detection. We've mostly stopped sending UHF transmissions into outer space and are now firing digital, encrypted, signals at the ground. Our detectability window might be as short as 70 years and, even then, inverse square law weakens our leaked signals to the point of indetectability, beyond a certain range.