I swapped my D800E for a D810 very recently and am still learning how to take advantage of it's benefits. At first they seemed to me to be minimal, I'm coming to appreciate that they are not in fact. Jack made a comment a while back that struck a chord, that he can't see anything replacing it any time soon for image quality (to paraphrase) for his use. I was really taken with the D800E coming from a D700, dynamic range being very high on my list of needs as an interior photographer. More is definitely better and I'm loving the seemingly improved color as well. In some situations the D800E made green go yellow to an ugly level. I'm pretty happy with the D810's greens overall regardless of the raw converter used.
I shoot tethered in C1 and make a point of satisfying my clients with a fit screen view as well as 100% mag. views of a given scene. The extra acuity isn't lost on me, having the low pass negating filter removed.
Pretty happy with the ability to actually judge sharpness (not just Relative sharpness) on the LCD finally as well. The D800E was a total mess at 100%. Incremental upgrade yes, but a worthwhile one to be sure.