"It means your $6000 camera just lost a whole load of value on the used market after a short time just because a camera with minimal extra quality/features arrives."
Tha tdepends on how you define "minimal".
Some examples from my real world experience with the D4s and the D4:
- If you shoot long action sequences you will definitely be glad that the D4s buffer is substantially larger than the one in the D4, which was already much larger than the D3s's.
- If you need to shoot with an absolutely silent camera the Silent mode at any frame rate advancement (Single, Cl (up to 12 fps) and Ch (up to 24 fps) is amazing - but you can only shoot JPEG Fine and the full frame resolution is binned down to 1,920 pixels on the long side of the frame ( not cropped, interpolated down). Admittedly the Live View Silent mode is also on the D4.
- When you have to shoot at ultra high ISO's, while the top two h4 and H3 ( 409,600 and 204,800 ISO equivalents respectively) are really usable but performance at Hi 2 and Hi 1 ( 102,400 and 51,200 ISO equivalents) are much better than on earlier cameras including the D4.
If you shoot wildlife, sports or any kind of action the D4s is a great camera.
If you shoot more static subjects like landscapes and portraits then a D800 is easily a better camera.