When i bought my D1 in 2001, it shot pictures at 2.74 MP. It still does. It took nice sharp photos then, and does so now, As long as it will do this, its not redundant.
I have moved up the ladder so to speak, with the changes over the past few years, in both Pentax and Nikon bodies. I don't consider any of them redundant, because i use them for different situations.
I kept my istD as a K10D back up, and i like it better for IR than the K10D.
I shoot my D1 and D1H for my equine work, and the D2H is now a backup. Why, because D1 and D1H have flash shutter of 1/500 which i need for indoor work, and D2H does not. Also its very noisey at iso over 250 i find, specially in cloudy days. D2H does better indoor general flash, so i use it for that.
D200 is a nice 10MP camera, but i like the K10D much better so it might go.
I think the only time i will say one of my cameras is redundant or obsolete, is when they break and i decide not to fix them.
Dave