Nikon Lens suggestions

Am thinking of getting a new zoom lens for someone for Christmas. Its for my wife, and we have a D40X and a 18-55 lens. My daughter has a Nikon and so does my brother. My daughter suggested the 18-105 VR, and I saw that for a bit more one could get a 55-200 VR. When I mentioned that to my brother he said he read a report that said the 70-300 had far better autofocus, etc, and of course it was a bit more. My daughter hinted that the 70-300 was on her list someday when she had some extra money to put into gear. My wife's 55 is no good at all for aircraft, but we don't want to buy a huge 2K lens for that or wildlife. Something in between is more our speed. Would like to hear thoughts by others who have Nikon's and maybe know about these lenses or others. Trains would be photographed as well. My thought was the 18-105 renders the 18-55 lens useless, but if we got the 70-300, the 18-55 would still be an option.
Greg Scholl
[www.gregschollvideo.com]