I have my eye on the D300 as well, Lee. I like my D80, but of all the Nikons, it has the worst metering system. All cameras have their quirks, it's just how long it takes you to find them and either work around them or use them to your advantage.
The D300 though is in a class that is new for Nikon. I have a number of friends that have them and they absolutely love them. The one thing that will be kind of a drawback is that the D300 uses CF cards, so you will be buying new media as well. I haven't seen anyone using a Bigma with the 300 yet, most use the 200-400mm VR (SWEET lens, by the way, but pricey).
I picked up the 18-200mm VR after I pranged my 28-80 on a door frame (long story) and LOVE that lens. The 18-200 is my air-to-air lens now and it blows away the 28-80 for clarity because of the VR. The 28-80 still works, but has been relegated to ground based duty for still life and flowers now. Although it rarely comes out of the bag these days as the 18-200 is awesome.