I am looking to do High Dynamic Range photography and am aware of the specs of the 2 camera models among which I am considering for purchase:
The Nikon D80 does 2 to 3 exposures in 1/3 to 2 EV increments.
The Nikon D200 does 2 to 9 exposures in 1, 2, or 3 EV increments

This having been said, my questions is, is there a notable difference between a photograph done from the addition of 2-3 exposures versus done with 2-9 - Isn't the latter one overkill?
What about using 1/3 of an increment, is it perceptible enough to create a significant difference in the end photo?

Thanks & regards.

Hey there, yes there is a difference. HDR images are images that cram a LOT of dynamic range into a photograph. A typical outdoor scene as perceived by the eye is about 10+ photographic stops from shadow detail to highlight detail. You will not be able to contain all this information within a few stops. That said, the camera choice is not relevant. The camera that does 9 exposures will give you a wider range at the click of a button, but one can create a HDR image by using a tripod and taking the series by hand (take a photo, adjust the shutter speed, repeat until you've covered the range (metered from shadows to highlights)) A good place to read up on HDR images (and see some stellar examples) is at the Munsell Color Science Laboratory's website located here: HDR Images & Appearance