If students are actually flying additional flights to work on other weak areas that's great. From what I remember of pilot training if you PAed through a ride you just flew one less flight than everyone else.
As far as I'm concerned, a dozen instrument flights is such little training already that even if you have a hot streak or just feel like you're nailing it, it's still worth it to see it one more time to solidify effective habit patterns and to potentially expose you to a situation you haven't seen yet.
When you're RTB low on gas, at night and in the weather from an LFE sortie that utterly blew your mind, you'll be glad you have good habit patterns to fall back on.