Goat;
Pay no attention to these non-believers... Heathens! The lot of them!
The years aren't so much of an issue. The basic design hasn't changed in 20 years or so. Personally, I wouldn't go in for anything more than five years old unless it was a monumental good deal. I would also stay away from the DRZ400, as it's liquid cooled, not air cooled. If you get out in some crazy stuff it's really easy to crack a case and then you're SOL. Parts are available for anything you can wish for, too:
https://procycle.us/ As for what makes the DR great, see below: