I agree with your first point, but I definitely would NOT let a wizard "use" the bat's blindsight. At best, I'd allow the familiar to communicate to its master the location of any invisible creatures it detects. Mechanically, the wizard wouldn't have to guess the target's square, but would still have the concealment miss chance from the invisibility.
ncG1vNJzZmivp6x7prrWqKmlnF6kv6h706GpnpmUqHyqutWiqqKamaG2tcWMmqWdZZKWwW6ywKagpaGRp8BvgY9raHBn