Lens preference is really an individual thing. But for me the Tamron 90 started out as an interm (Had $275 and got a LN- from KEH). Well, I love the weight and the optical performance.
I have my share of Nikkors: 12-24, 24-85D, 80-200, and 300 AFS), but the Tamron 90 f2.8 is such a great lens, I don't think I'd get ride of it even if I got the 105VR. The light weight and how well it works with the KenkoPro 1.4 makes it a great system.
Now if I already had my D200 (which I am several weeks away from ordering) already I might get the 105VR because I have the 1.4/1.7 TCE, but honestly I can't say I've seen any optical performance on Macro shots that are better than the Tamon. Yet many say if OOF details are much nice than the Nikkor.
But as I started this post, I really do understand what you are going through. I shoot mainly with my 12/24 or 300. Yet I need zoom. Started with the 70-300ED - too slow for sweet light. Then I got an 80-200 f2.8 2r, great, great lens but gets used mainly on vacations.I thought about selling it and getting a 70-300VR, but you know what, after shooting with it I love it and even get very good results with the KenkoPro. Go for the 105VR if the cost doesn't matter, I'm sure it is a great tool.