You might be missing the point of the higher end body. Comparing shots between the two is going to do nothing for your decision. Virtually any DSLR is capable of capturing almost identical images. The biggest thing the higher end model gives you is an easier or more convenient way of doing it. For example, the D80 has two knobs to adjust the shutter and aperture where the D40 has one. That makes it faster and easier to change both when needed, but the cheaper body can still do the exact same thing. Most higher end ones also take burst shots quicker for more shots, which give you a better chance of getting the best shot. Again, the low end body is just as capable of doing it, but you need to have either more skill or luck to get the best shot. Some higher end models have a more usable high ISO, but that does not come into play between the D40 and D80.
There is aways the focus motor situation between these two models. The D80 will AF all of the AF lenses where the D40 requires the lens to have the focus motor. The D80 allows you to get the ~$100 50mm f/1.8 where the cheapest fast lens that will AF on the D40 is $400. Both will work great. That decision comes down to how much you are willing to pay for a lens.