To be honest you have to be careful not to fall into the same trap as Home Cinema freaks and DIY PC makers can.
The numbers game.
Just because the spec sheet and a few snazzy graphs look BIGGER and BETTER and HIGHER than older models doesn't necessarily translate to better sound, a faster PC or better pictures.
A pro photographer with a disposable camera could probably get better results than you or I with the latest greatest Nikon!
If cost is an issue I would go for the 18-200 lens and a cheaper older body. (A pro would shudder at the distortion that you or I would not notice and recoil at the thought of this lens and swear that you need many different lenses specializing at different ranges!)
The huge number of megapixels on the D90 and similar is just gonna eat up memory card space, hard drive space, increase download times and you will need a faster PC to process the images.
If you are not going to be PRINTING OUT images >A3 size then you would be better off going for no more than a 8 megapixel camera, allowing you more to spend more on the lens.