Is now a good time to buy a 2nd-hand digital SLR?

Right, think this is the right place to post this. Serves as a good test too for those looking at this forum for the first time.

So the crux of the issue is this. I’m a non-photographer with an “ancient” Fuji6900 but don;t want to fork out another £600 only to see it become virtually worthless after 18 months. With Nikon D50, D70, Canon D350 and upward coming out, would now be a good time to buy the previous version of said models? Please discuss.

Off to gander at e-bay. Is there an attractivce price advantage I wonder?