Carbonaceous chondrite asteroids are often over half hydrocarbons. Think oil/coal in space with lots of water to make rocket fuel (oxygen/hydrogen).
Nickel-iron asteroids have up to several percent platinum group metals. Some are almost pure enough to smelt into stainless steel. No doubt, some will assay higher than others. Out of millions of asteroids in the Solar System, there’s probably one with a bunch of gold in it.
Even silica chunks can be useful if you drop them on Iranian nuke installations. With a big enough rock, they cannot bury that sucker deep enough to escape.
BTW, I think I have met some of the principals in these mining endeavors. I think I am still listed as an Adviser on the AIAA Space Colonization and Utilization Technical Committee.