Upload & Sell: Off
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?