What if millions of years of advancement wound up leading to very, very different goals for colonization than what we're used to based on pretty much nothing else other than fairly recent (by comparison) human history?
What if, for example, if you're a civilization that's been around for millions of years, your goals are no longer to "extract base resources" like in "Starcraft" ... but rather to play a sort of "Sims" game where you guide the development of life on various planets and "extract" research data – or simply sit back and enjoy the show?
Or what if they have an advanced Ai they're testing and want to see if life on colonized planets turned out like the Ai said it would, and if so – to what extent?
In that case, the "resource to be extracted" wouldn't be physical as much as knowledge and possible entertainment.