First my assertion that aliens wouldn't want planets is based in reality, we keep talking about planets that have life being colonized but to do so would require a planet that is quite a bit more than life friendly. So far no planet we have found out of the several hundred to a thousand or so planets we have found could support humans, a handful might have life but if you give it some thought a planet would have to be far more than just the right temp. I see no reason to assume a "Goldilocks" planet would be inhabitable, gravity that was much beyond earth normal's would be a problem but not insurmountable, I am sure there are reasonably close sized habitable planets, air pressure could be a problem as well as could ratio of atmospheric gasses, I am sure there are others not the least of which is our planet rife with heavy metals? Even a slight difference in the abundance of mercury would make a planet uninhabitable to humans.
My point is that once you realize just how perfectly we are evolved to the earth it becomes apparent that a "drake -esque" calculation must go much further than a planet be the right temp for liquid water, the variable are tremendous in number and there is no reason to expect "Earth like" to mean habitable. In fact so far the "Earth Like" planets we have found are super earths, high gravity and thick atmospheres, I know the sampling method is skewed due to smaller planets being harder to find but the variables are far more complex than temps and size.
The reason I suggest orbiting habitats would pursue the resources of places like the ort cloud or Kuiper belt is that while you are correct that they are mostly ice that doesn't mean they are all ice and if you live permanently on your space ship/home world the distances between the individual objects become less important since you only visit them when you need more water or metals or helium 3, deuterium, or maybe trace elements that are difficult to recycle or are slowly lost due to leakage from the habitat...
And yes those objects are mostly ice but they contain enough rocks and metals to be useful and rocks and metals would be a very minor component of your colony, I think advanced civilizations would be more likely to construct things out of Carbon fibers and various other non metals than use large amounts of metals.
The main endeavor after survival of the colony would be to make another colony, no need to visit the dangerous radiation zone near a star and if my scenario has any validity we should be looking at stars with large amounts of material orbiting them not looking for sun light stars. The type of colonies could utilize the environment around any star not just sun like stars... Fomalhaut and Vega come to mind but this approach could mean we are looking in the wrong places for life.