As a user of a Nikon D800E, yes, I think the "full frame" thing is about 75% hype (maybe more.) When I'm on vacation or taking photos in a city (usually that's the same thing!) I mostly use a small Nikon D5300 with small lenses. Or if in a very grungy dirty city (Chicago, San Francisco) I prefer to use a Nikon F3T or my Leica IIIc with b&w film! So why keep the D800E? Mostly for three reasons: (1) weddings. I do like the bit of extended dynamic range in tricky light. (2) portraits (and other paid work.) I can make very big enlargements, for which I charge more. (3) tilt/shift lenses. Not aware of any smaller cameras that can take wide angle versions of those, and my 24mm PC-E is my favorite lens of all! What I would love is a small camera system, with Leica LTM sized lenses (or even Nikon AiS) that offers a couple of fully functioning tilt/shift lenses. I can't live without them. But yes, I think the "full frame" deal is way overhyped.
All these points are very relevant, but any comparison between the qualities of a cropped format and a full-frame format should exclude all features which are not directly related to the differences in format size.
Comparing different brands of cameras introduces a whole range of different features which are not related to format size. The only sensible comparison is between two different formats that have the same size and quality of pixels and which can use the same lenses.
The closest example I'm aware of is the 16mp Nikon D7000 cropped-format compared with the 36mp full-frame Nikon D800. The pixel quality and pixel size is almost exactly the same for both cameras.
So let's consider the advantages of the D800 in such a comparison.
Let's compare how the two cameras perform with a single prime lens such as a 50mm F1.4.
(1) The lens on the D7000 is effectively a 75mm prime. However, in relation to the general quality of the image that can be produced by the D7000, the D800 provides an exceptionally high quality 50-75mm F1.4 zoom.
How much would such a zoom lens cost, if it were available, and how much would it weigh?
If such a lens were available for the D7000 it would be a 33-50mm F1.4 zoom.
(2) A similar situation applies to all full-frame lenses that fit the two cameras. Let's say your favourite lens is a 400mm F2.8 prime for bird shots. On the D7000 it becomes an impressive 600mm lens. However, on the D800 it becomes an even more impressive 400-600mm/F2.8 zoom, in relation to the maximum image quality of the D7000.
To get an equivalent range of focal lengths on the D7000, you would need a 266-400mm/F2.8 zoom. I suspect that the weight of such a zoom plus the D7000 body would exceed the weight of the D800 plus 400/F2.8 prime. Not only that, the quality of a zoom lens at every focal length rarely matches the quality of a good prime lens at the same focal length.
Also, when downsizing the D800 image at 400mm to match the size of the D7000 image at 266mm focal length, both the noise and sharpness of the D800 image will be better. If one considers such an improvement insignificant, then that's fine, but that's just a bonus in addition to the free conversion of all one's prime lenses to short-range zoom lenses, and the conversion of all one's zoom lenses to extended-range zooms at the wide end.
However, if one is comparing a cropped format which has smaller pixels, but of approximately equal quality to the larger pixels of the full-frame format, such as the D7200 compared with the D800, then the cropped format will have a resolution advantage with the same lens, but I doubt such a resolution advantage would be significant comparing the D7200 with the new D850.