And those are more easily obtainable from asteroids, where planetary geology hasn't dispersed them, and you don't have to contend with a massive gravity well.

There isn't anything that you can get from a planet with life that you can't get elsewhere without expending the resources to go there in the first place. Except for life itself. It's actually far more likely that other species would be infinitely more valuable as a source of study than for any material resources.