the 18-105mm is sufficient or better to have the 18-200mm VR.
Tamron 18-200, which is a cheap lens (though you have to make sure it's the one with BIM (build-in-motor) version as there are quite a few, the difference is in marking (12, 14 or so, which indicate the version of the same lens). The cheapest one is without motor and can only be used on D70, 80, 90, 7000 on "budget" models, does not have VR/VC. 18-200 is the oldest out of bunch, it used to come as part of the "travel kit" consisting of 11-18 and 18-200 (had both, kept 11-18). If it's worth anything, I had (and still have, but broken) SIgma 18-200 OS HSM. Sigma was optically much better, it had its weak points at particular focal length and other few where it was brilliant. Overall, it was much sharper as Tamron 18-200 is consistently soft. Another thing about "super zooms" - being varifocal lenses, the "200mm" is that only at infinity. At 100ft, they act as only 135mm (compared to "true" telephoto" lens, so for example 70-300 "is that" while 18-200 "is, but conditionally". You mention 18-200
VR , which refers to Nikon lens. That lens IS much better than Tamron 18-200 but costs way more than it.
I tried Tamron 18-270 PZD VC - stabiliser works very nice, it's fast to focus unless zoomed 180mm+, where my camera can't decide about focus and keeps hunting, unless really bright day outside. Perhaps newer models (D7K) have less issues with that lens being 6.3 at those focal lengths, I wouldn't know. Optically, that lens is way better than 18-200 ever was, despite its shortcomings.
I still think that 18-105VR is an excellent lens for the money - I bought mine for AUD$125 second hand as there is an oversupply of these lenses due to Nikon having 2 late models having it as kit lens. "White box" 18-105VR new is sold around for $245-275. Nikon 18-200VRII is 3 times that amount and you can actually get 18-105VR and 70-300VR for less than 18-200VRII alone. It may look like hassle, certainly much better combo as photographics tool.
BTW, I sold my Tamron 18-200 for AUD$95 just few days ago (and I don't think I'm at the loss here, that is what I think about that piece of glass. YMMV)
cheers