The older lens was designed when Nikon did not have a FF Body, and when the FF body came out, there were a lot of people who were unhappy with its high price and performance on FF. On a Nikon Crop body it is supurb, so no need to think about upgrading unless you are moving to a FF body.
Canon's has been increasing both lens and body prices to the point where some high end Nikon lenses may cost less. However, if buying new lenses, I'd pass on the "D" lenses with a mechanical screw drive. They are always going to focus slower than the "G" lenses. If you are buying used lenses, as long as the price is right and you have a body that can drive them, they will fill in gaps in focal lengths that are not used everyday. Nikon has not necessarily replaced all those old D lenses with G lenses yet either, so you may not have a choice. Many third party lenses are screw drive, but third party lens makers are producing electrical focus lenses as new ones come out.