As you said the Drake equation is little better than a starting point for a very loud discussion of astro-philosophers. On the other hand it does give a framework to start making guesses, and as we continue expanding our knowledge about the universe we can determine limits for either some of the terms or for the final product.
From empirical evidence we know that the Drake equation has a lower bound of at least 1.
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From empirical evidence we know that the Drake equation has a lower bound of at least 1.