I'm at the same point with my Dark/Dark so I don't have any specific advice just yet. But one thing to look at when deciding on what to buff for a power is the strength of that portion of the power. For example, Twilight Grasp has a 5% ToHit Debuff while Fearsome Stare has a 15% ToHit Debuff. You're going to get a bigger bang if you slot up FS especially given that it's also an AoE, and you're not sacrificing on the other aspects of TG (the Heal). Now I'm not saying that's the best slotting for FS, but it's a possibility that I'm contemplating (with the Fear just along for the ride or many 1-slotted with an IO for another set).
