For travelling, don't forget the housing for the d2x will be bigger/heavier too, not just the camera.
I realize there is a difference, but it's not like the D200 is a P&S and the D2x is Howard Halls Imax camera

Is your travel really going to improve dramatically packing a 1lb 13 oz body rather than a 2 lb 6 oz body? Your hiking might, your biking might, and perhaps if you routinely carry two bodies slung around your neck....that might, but otherwise the gear in question, packed for carry-on or checked baggage, isn't going to make a difference distinct enough to base the choice on.........IMHO

If price is not a consideration, is the weight and size difference between the D200 and D2x really equal to the diminished photographic capabilities inherent in choosing the D200 that would otherwise be applicable to your type of topside shooting? UW the D2x advantages disappear to some extent, but the OP said he was going to shoot aviation images and the hi-speed crop mode along with the better AF of the D2x would be lost to him if he chose the D200....and all because of a couple pounds. That extra 3 frames per second, stronger more sensitive AF and more powerful focus tracking is probably a nice capability when planes are buzzing by.
One of the nice things about the D2x is that it's a pretty good sports camera hidden inside a flagship model 
I am not disregarding what a couple pounds could mean, but when considered in light of his wish to use the same body for topside work, and topside work that is more specific to D2x capabilities than D200, I don't see where the minimal weight disparity is an equally important consideration.