I actually kinda liked Rocket to Insanity, at least in comparison to Cupcakes, because it at least tried to make a little bit more sense.
(If you haven't read it, basically the events of Cupcakes are part of a vivid recurring nightmare that Rainbow Dash keeps having. The visions of her own death drive her insane to the point that she lashes out and kills Pinkie 'preemptively'.)

To me, though, a sequel doesn't really seem appropriate. It was the misunderstanding and irrational panic that created the tragedy in the first one. Having her just go on a killing spree now seems unnecessary. It feels like a sequel for the sake of a sequel and not because the storyline demanded it.