Stacking sounds like it would be a good idea, but It should have diminishing returns. Also The buff should apply to each individual buff in the stack, so it decays over time. That way there is an extra sense of urgency if you want to use it, and at some point continuing to build that stack no longer provides benefits.
That's what I was thinking as far as stacking is concerned. Separate buffs with decaying returns so there's a point where adding another kill isn't worth the time spent looking for one.
If they don't make it stack even a small amount what is stopping people from just finding a rare or champion mob to kill and then skip to the boss? Without it stacking I don't see the problem being fixed.
Yeah, I just assume it'll stack at least a little. I mean, otherwise it's "kill Unique on the way to boss chamber" and that doesn't solve anything besides a momentary speedbump.
I think the most important part of the buff, though, is the fact it gives you more loot drops. If I'm reading that right, anyway, that means with the NV buff you'll get 3 drops instead of 2, for instance. That alone makes it worth killing at least getting the buff going.