When it comes to Nikon, each new generation seems to be excellent. The specs and review of the D800 were impressive. But after lurking in the D800 sub-forum it seems not all is well (quality issues, focus problems).
I had the money in hand to buy a new D800, but decided 12MP was enough and that commonality with my D300s was more important than having the new thing.
As a hobbyist, the D300s and D700 represent more-than-adequate tools. And to your four points, there isn't much (that I need to do) that a D800 does better than a D700.
I know there is a desire to have the latest thing. That's not wrong. It's the people who want better tools, that drive the people that make them. But I've decided that wanting the latest thing for it's own sake isn't how I'm always going to play it.