It's difficult to imagine a discovery that would have more practical import than the discovery of an extraterrestrial civilization.
Why, yes, of course - even in the immediate short term the ships returned from expeditions with gold and slaves; and from the very start the exploration voyages were planned and funded solely as a practical endeavor for trade and looting, not as an intellectual curiosity.
But anyway looking for Dyson spheres will not reveal any extraterrestrial civilizations.
To make the point, literally nothing can be classified as "discovered" under your rules because any alien civilization may know about everything we'll ever find or figure out, and if they know about it we can't have discovered it.
Columbus was a murderer and people in America before he got there deserved way better but this type of nitpicking correction is just noise if you don't even say what is a more appropriate phrase.