Yet Robau's crew never seemed to think that firing back at the projectiles would be necessary
They didn't HAVE to think about it, it was the very first thing they did when the Narada fired at them. More importantly, they WOULD have been considerably more effective if the missiles hadn't split up into a dozen small and powerful submunitions and hammered the ship like a steel rain.
I've actually been sort of pondering two things from STXI.
1) Could/should we re-imagine "shields" from being a skin-covering forcefield and change it into the name of Starfleet's standard CIWS system? That would certainly explain the lack of visible shield flares in the movie and the fact that Kelvin continues to fire phasers even after the engineer tells Robau their weapons are offline.
2) Narada's torpedoes are described as "powerful and advanced" but there doesn't otherwise seem to be anything special bout them other than the clusterbomb trick. Maybe that singular innovation IS the thing that makes them powerful after all? Certainly WE'VE never seen anything like it in Trek, and Kelvin's engineer might be referring to the fact that Narada's single torpedo blew through his engine room in about a dozen different places at once where a normal torpedo only would have hit one spot and been quickly bottled up by STI fields.