I think that the real issue is that the 18-200 3.5-5.6 G DX is not a very sharp lens. My experience with that lens is that is not capable of the critical detail that you seem to be looking for.
I have been very disappointed with my 18-200 at 18 and 200mm, and especially macro at 200mm. The in-between focal lengths and distances can be ok especially at f/8. I read a post by a Nikonian team member a few months ago that the 18-200 NIKKOR lens was not as good optically as the 18-55 or 55-200 "kit lenses" so I tried some macro shots of a cone flower with the 18-55 and had fine detail in the flower that the 18-200 only had fuzzy edges with. I used manual and auto focus with both lenses on a D3100.
Try those same shots you had with the 18-55 "kit lens". The 18-55 focuses very close and will reveal detail in the photo that the 18-200 can't come close to.