I can't really fall out with any of the very comprehensive comments you make. I too am fond of old shoes and I guess my D700 falls into that category too.
<<I'm just arguing here that the high end body world is headed into two FX cameras, one a "studio" camera like the D800, but with the DX frame rate many of us want, and a lower density FX camera suitable for things like sports at 8fps or better.>>
No, I don't expect Nikon to invest in a low market APS-C camera without financial benefit, but I think they are playing a cunning marketing game. Maintain the D300s (in the UK even the D90 is still current) until a respectable fps FX camera is developed. That may well be the rumoured D600. When that happens bye bye D700. If it is a D600 and it has enough pixels to create a D7000 file size in DX mode then bring it on. However, we know the higher the pixel count the lower the fps due to buffering speeds. So, is this a viscous circle - increased pixels = lower fps.
I am not against, either by habit or stubborness, technology that meets the criteria I need. As an electronics and communications engineer for more years than I choose to remember advances in technology was and I still have a natural apetite for it. In all the projects I managed I always needed to be convinced that the investment was worth the result. The same rules apply to advances in photographic technology with an even bigger reason, this is also my money!
I don't think I'll favour the D800 as the FX side is currently covered to my satisfaction with the D700 at present. It's the DX (fps etc, etc) side I'm interested in and when that is addressed, in whatever guise a future FX camera takes, I shall welcome it and embrase it. Thanks for all your comments and they are extremely thought provoking.