Er, yes I got a lovely D80 second-hand from someone with your identical name, its only drawback being the difficulty of cleaning it.

Unless you are prepared to change mode completely from light to heavyweight, I wouldn't have thought a D200 that advisable. Big lenses have trpod mounts, which can be used as a handgrip or placed on posts or rocks. The argument of balancing lens and camera doesn't grab me. If you had wanted any of the few features not on D80 you would have got a D200 as no 1?

Have you won the lottery (Nikon 500 prime!)?

I now have a 1 body solution for most of my photography, viz D80 with Nikkor 80-400 and canon 500D close up ring. It hardly ever comes off except in town or indoors where the 18-135 kit comes into its own. But then I am not into the v wide-angle landscape approach that is in fashion (and like all fashions will pass).

I don't think the sensor dust comes from lens changing as such - it seems to either lurk within or is even generated within by very fine abrasion fragments. Its worth making sure inside of body-end caps and lenses are really clean before putting them on, likewise Sensorscope if you use one to view the muck. An artists sable brush charged up by rubbing on a clean piece of wood seems quite good for removing visible fragments from each place. The sub-visible residue can be dealt with using dust-off function using camera+capture NX combination