I think it's one of those things you just have to experience for yourself. I've been shooting portraits with a D3X for several years now and while going from 24MP to 36MP seems like a lot more, it's only slightly more than 20% more pixels in the linear sense. Not too big of deal. Portraits made with the D3X are easy to retouch because I can stay zoomed out a bit and work with larger areas (arms or cheeks) or zoom to have fine control over the eyes. If you take advantage of the many plug-ins out there for retouching skin (Nik, OnOne, etc.), you can get through the operations quickly, especially if you've done light retouching on your original image using LR, ACR, NX, etc. The bottom-line: it just hasn't been that hard, and I can't see another ~20% pixels breaking things. Also, my quick retouching operations have also been sanctioned by my wife, and she likes the portraits I've made of her. That should say a lot.
Also keep in mind that lighting can either enhance or supress fine detail in the skin. This specific shot was made to have the viewer think "holy moly, that's a lot of detail". You may not see as much in other shots depending on how you set your lights.