I am the owner of a Nikon D200 and an assortment of DX lenses. I am considering upgrading the body to something better, but I am hesitating for a few reasons.
First of all, I am reasonably satisfied with the D200. My main gripes is the exceedingly bad battery life, and the now surpassed high ISO performance. Of those two, the battery life is the worst. I never get more than a couple of hundred exposures before a recharge is required. I bought a second hand MB-D200 battery grip, but I was very disappointed to learn that the it actually depletes the batteries even when the camera is turned off. Battery power is used to brighten the viewfinder display. This is impossible to turn off, and I have to take the batteries out of the grip to prevent power leakage.
Secondly, I do not see a clear upgrade path. The D300(s) is too similar to justify the cost, and the D700 would require me to upgrade the lenses also. I have seen rumors of a D90 replacement coming "soon", which may or may not be relevant. Video, on the other hand, is not important to me.
I always thought "wait for the D400", but playing the waiting game is hard.
What would you do in my situation?