From a perspective of pure math, I think that is the same thing, but in considering practical computability, it does not seem like a good use of computing power to figure what weight to give the preference of a particular alien civilization out of a vast space of possible civilizations, until observing that the particular civilization exists.
One such regularity comes to mind: most aliens would rather be discovered by a superintelligence that was friendly to them than not be discovered, so spreading and searching would optimize their preferences.
From a perspective of pure math, I think that is the same thing, but in considering practical computability, it does not seem like a good use of computing power to figure what weight to give the preference of a particular alien civilization out of a vast space of possible civilizations, until observing that the particular civilization exists.
Such considerations could have some regularities even across all the diverse possibilities, which are easy to notice with a Saturn-sized mind.
One such regularity comes to mind: most aliens would rather be discovered by a superintelligence that was friendly to them than not be discovered, so spreading and searching would optimize their preferences.