Were you shooting in auto, or did you try using different settings indoors, outdoors etc.
Each camera will have a series of settings that will make it look "good" in differnt situations. The appearance of an image also can be very subjective. Each person has their own preferences as to color saturation, contrast, yada yada.
I've been doing a couple of tests between my D50 and D80 and have come to some pretty interesting and startling conclusions. Look at the sample below before reading further to see of you notice what I do. I've noticed these same things in other locations not just my lil makeshift studio.
If you saw what I did you noticed that the D50 is better noise wise and shows a bit more detail than the D80. All settings were identical. Custom optimized settings in the camera setup are identical. Shutter was set at 1/125, aperture was at F16 & ISO was at 400. Camera's were set on the same tripod and triggered with the same IR remote. Same lens was used on both bodies as well...my 18-200vr. The same flash was used at roughly the same position...my Vivitar 285HV at 1/4 power with a lumiquest softbox attached connected to the hotshoe via a coiled sync chord.
Doing casual street shots I've noticed that the D80 also tends to over do it in the shadows giving them an "inky" feeling...a problem I never had with my D50. The D80 seems to have the subtle noise/grain look on the street as well...even at ISO 100. I looked at other peoples' test shots on the D80 and have noticed the same noise/grain look. While the D50 looks like butter at 200 all the way to 800.
I'm not sure why Nikon didn't just use a higher resolution version of the same sensor used for the D50 in the D80 and give all the enhanched usability features that the D80 brought.
I find myself torn now between the D80 I just purchased and the D50 that I've agreed to sell to a buddy of mine to offset the cost of the D80. The D50 is just so good that it crossed my mind to ebay out the new D80 and stick with my lil buddy D50. The only thing that keeps me thinking twice is the enormous (compared to the D50) viewfinder view, the huge 2.5 inch screen, more hardware controls and commander mode. If I could somehow get those features into my D50 I would be happy...6mp is way more than enough for 4x6 prints...heck I even got nice 20x30 inch enlargements on our large format HP at work from 6mp....10.2mp is a bit overkill for anything but posters & heavy cropping.
I've tried tweeking the settings to get closer to what I got used to seeing with my D50 but still haven't hit on the mark. I'll keep doing my tests to see if I'll be keeping my D50 and selling off the D80. I might have to welch out on my buddy with my D50.
Just a thought, if you think the D80 over-processes the image, and you are using iso400 or above, then perhaps adjusting the high ISO nr would help.
I took a look at your test images, and I think the differences are minute (I don't think they will show up on print). If D80 is good enough for you image quality-wise, and it handles better (viewfinder, lcd, front dial...etc.), then why not keep it.