In terms of colonizing other star systems, wouldn't small objects like asteroids, moons, and dwarf planets make more sense to develop, as their low escape velocities mean it would be easier to extract and launch resources in space to be used on-orbit?
A colony ship immediately investing all of their resources into trying to build a self sustaining civilization at the bottom of a deep gravity well would make progress difficult, as they'd have to spend much more effort trying to synthesize fuels in order to shuttle mass back and forth from surface to orbit and vice versa, as well as requiring much more complex and difficult to build rocket systems. By contrast, a colony ship using several asteroids or moons to gather resources would be able to use relatively simple propulsion technology and wouldn't have to spend much time producing propellant as not much would be needed by comparison.
We already know that every element we use on Earth can be found in much greater concentrations and in much larger quantities than here on Earth, so why wouldn't the case be the same for other solar systems?
Maybe trying to find and study Earthlike planets has little or nothing to do with eventual colonization efforts. Finding asteroid belts and other small objects is probably far more important.