The most accurate, currently used ICBMs can have a CEP ranging from 10 to 130 meters so they can probably be used that way. Most ICBMs also have a configurable "detonation" height, meaning they can probably be set low enough to severely damage a nuclear plant reactor containment building. Not sure if they are powerful enough to vaporize the fuel rods though.

But as you said, at that point, it wouldn't really matter anymore.