I have owned a D700 for several years and then a D600 for about year. I ended up getting a D800 (mostly due to sensor issues).
For me and my style of photography (wildlife, astrophoto, travel photopgraphy, landscapes, cityscapes, macro, family - all amateur) the D600 clearly is a much better camera. In fact when I look at my old D700 RAWs in Lightroom I often think about how great it would be if I had a chance to reshoot them again with newer gear. The pictures I had to bracket, stitch or filter on D700 can shoot straight away now. Shoots that would have been lost due to exposure or dynamic range of the scene can be recovered now, much more headroom for post processing, less colour shifts, cropability, etc.
However, I am sure there are people who shoot different genres (sports, action, ...) who care about frame rates, AF speed, can't afford missing a frame, etc. These will probably think the opposite. Luckily, I don't make my living on action photography
So think about what you shoot and then decide.