Hi,
Personally, I'm still picking up the Kodak DCS series here and there as the price is right. My reason is not for collecting. Those who know me around here know I'm the oddball that buys this stuff to use it still.
The Kodak 6 MP models are unique in that they give us Kodachrome color, and are all that's left of that now that the film itself is dead. I know that there are no parts available anywhere for these things, and I have to support them myownself. So, I pick up what I see going for cheap, as they form a supply of replacement parts.
I have no reason to go to something with greater resolution than 6 MP. I had started down that path with a Canon 1Ds back when they were still the hot ticket, and then backpedaled to the Kodak DCS 560 because I like the Kodak color much better. Since I don't print beyond 13x19, and usually 5x7 and 8x10, 6 MP is good enough.
It's not just the digital imaging parts I want, either. I know that the Canon and Nikon camera bodies are modified from their stock form for use with the Kodak digital backs, so I need the camera bodies for parts equally as well.
I still wish to pass down the Leica DMR road some one of these days. That's the 10 MP updated version of the Kodak imager used in the DCS 760 and represents the pinnacle of that particular line. Then, too, I'd like to have a Pro Back Plus as well, which gives yet a different view of things, as it were.

Anyway, I did pick up a couple extras during this particular glut of units onto the eBay market.
Later!
Stan