First thing first, all of your images are excellent in quality. They are all well exposed and rich in details.
The D800 is a great camera. As you have seen the RAW files are huge requiring more memory and extra work. I use a D610 with 24 megapixels and I feel that the RAW files are huge also. It is also an excellent camera capable of fantastic results.
Full frame cameras are very good for low light work because of their performance controlling noise. Modern APS sensor are pretty good also in that respect. We favor full frame because the focal length of lenses did not share the digital factor that cropped sensor cameras do. Today things have changed and we can find excellent extreme wide angles to work with those cropped sensors. When it comes to using teles the APS sensor gives the advantage of "longer" focal lengths.
I enjoy shooting with both but when it comes to quality I cannot see the difference between both sensors.