Upload & Sell: On
In no way is this intended to sound disrespectful, but if you do not own or use the D800E, it may not be fair for you to state there is a "tiny marginal improvement" over the 5D2. From my experience, there is a noticeable and substantial improvement in sensor quality in the D800 over the 5D2, which I also own and still use. Additionally, as a side note, for working photographers in fashion, many clients demand higher megapixels (36MP+). In those instances, "need" is definitely appropriate.
What seems to escape notice is that it is far more the photographer than the camera that defines how good is the landscape.
I was poking a bit at OP's choice of words "need to buy."
I have no problem with someone saying that the extra pixels of a D800E (and the better DR) will make a difference in the way he/she shoots/processes/prints his/her landscape photos, but "need"? The tiny marginal improvement in anything that the D800E has over the 5d2 for landscapes hardly arises to the level of "need."
Any other questions?