Yes, they did consider hull separation for other occasions than just emergencies.
Well, the makers of Star Trek did. There's no evidence Starfleet did, in-universe.
Even the quoted text makes it sound as if the stardrive section is not fully equipped and cannot operate independently, but must wait it out with a small supervising crew aboard when the saucer is having fun elsewhere. Whether the saucer can move around at warp/FTL is also left undiscussed.