Chris,
I assume by "200 VR" you are referring to the 18-200 VR vs your current 18-135mm lens. (Some may have thought you were referring to the 200 VR f/2.0 lens)
I own both lenses. I bought the 18-135 lens to use with the D40 because it gives a good all-around range that fits the camera better (size-wise) than the 18-200 VR.
I bought the 18-200 VR lens not long after I purchased the D200. Those two are truly a good match from a size and balance viewpoint. Of course, the 18-200 VR lens is a good match for any of Nikon's DSLR cameras and it will certainly work nicely with your D80.
From a quality viewpoint, I would say that they are really very similar in their overlapping ranges - from 18-135mm. At the wide end with the 18-135mm you can get a little bit of color fringing that is evident when shooting high contrast items, like window edges when shooting from indoors to outdoors, etc. This is a very minor issue for me and is easily corrected if I find a problem with it.
The 18-200 VR is a very sharp lens throughout its range with the weakest part being at 18mm (as is the 135mm lens), It has some barrel distortion at the wide end and a little bit of moustache distortion at the long-end, but neither are enough to bother unless you are looking at a serious pro photo requirement.
From an all-around lens, there is no doubt that the 18-200 VR is simply the very best travel do-all lens that Nikon makes. The difference between 135mm and 200mm is significant if you need it to catch that long distance smile or frame the landscape shot you really want. VR is also outstanding on this lens. VR is less important up to about 135mm, but once you get longer, it is very helpful in reducing camera shake issues, especially at lower shutter speeds.
Based on my experience, I think you would really enjoy the added range and VR feature of the 18-200 VR over your 18-135mm lens. You could easily sell the 'kit' lens because it is still very popular in its own right and I don't think you would look back at all.
Regards,
Paul
