I think you are all missing something huge - Night Terrors aren't insignificant. We'll get back to that in a moment.
They fly 6" for a walk and can pull others for a 0 action - this translates into an 18" range, guaranteed. I've seen the Cerebus noted as "ridiculous" for being able to move 19" in a round. But here, these little guys don't have to cast to do, can fly for the whole movement and are significantly cheaper to boot. Their "Attracted to Noise" is just gravy.
They're not exactly fragile, either, especially for the cost. At ht 1, fast and mobile, they're easy to hide. But their DF and WD are both solid, and their other abilities round out these characteristics to make them not so easy to bring down, played well.
So why do you care, Master Marcus? Let's take a look at the new Schemes, shall we? You mean the Arcanists have two schemes that require models to get to remote portions of the board, for lots of victory points? Ah, but they can't be completed by Insignificant models. If only we had cheap, non-Insignificant models...