My first digital camera was the Pentax K100D which was the equivalent of the D70. I've had it since 2006 and it's still a very good camera which captures very nice images. From time to time I still shoot with it. I've kept it because of the CCD sensor, which tends to be a bit more saturated, with nice large pixels - it just does a really nice job. The images have a very nice "character" to them.
Over the years, I have upgraded - but I have found that the new equipment is great, fun to use and does a really nice job - but the old equipment can be just as capable, depending on what you use it for. It does have limitations for some uses like astrolandscapes, etc.
A number of years ago, right after I upgraded to the K5 (16MP), I decided one Saturday afternoon to take a run up to the Grand Canyon - just a little 5 hour drive to shoot the sunset. Tossed everything in the truck and took off. I got up there and was shooting, then all of a sudden my new k5 drained my two batteries (it turned out that the mirror motor had a short), so I went back to the truck and picked up my "old" K100D, and kept shooting. After getting home and comparing shots the next day, the K5 had nice detail, excellent image quality, colors - everything was excellent. But, the K100D also had really nice colors, saturation, nice detail - the K100 kept up really well.
I learned a valuable lesson that day - that old equipment when used right can be just as capable. There are limitations - you can't print as large, with CCD you are not going to have exceptionally high ISO values to use - but for a lot of your shooting you can still do really well.