I've been reading and thinking about the replies in this and other various upgrade threads. Unfortunately it's given me a panic attack .
The basis of the attack is "where is this all going", "what am I going to do when my D700 wears out", "should I buy another D700 now", "is there a plateau and when is enough, enough", "What me worry?".
Sometimes these second order speculations (speculate on the speculations) are fun. This is the first time I'm thinking that at these $5-7K price tags, there needs to be a point at which the technology and interest can survive for much longer than just a refresh cycle. The current business models doesn't support that and at some point (maybe after this cycle) there is some cash in Nikon's bank to weather the plateau.
Anyway, this is likely totally unintelligible by now. My crystal ball is broken.