When your diff blows up all over the track, you know you needed it.
Honestly, whether this thread is in the right place or not, I'm thinking about it too. My thought is that if you're not tracking the car, don't worry about it. If you are, it's probably worth getting one (or just step up to a new diff, which is what I'm seriously pondering). Nissan didn't put them on their press cars for no reason...
Maybe the best option is to just leave it as is, let the stock diff melt down, and replace it when it does...
Anyone know how much a quaife costs fully installed?