so i have the d200... and i hate it! it seems soft and is awful with noise. have you tried your d700 in low light and high iso's? i would love to hear your thoughts!
I also have a D200. I do NOT find it soft, even with a lens known to be just a general shoot around lens (the 18-200):
http://www.flickr.com/photos/jerryph/sets/72157604136892371/show/
Noise? Ok, its not a D3, but, I don't have issues at higher ISOs when properly exposed and using some noise remover apps when needed. A few ISO 1600 shots:
http://www.flickr.com/photos/jerryph/sets/72157604515421416/show/
A lot depends on how you set up the camera, the lens, what format you shoot and how you post process.
I would go so far as to say that if you cannot get great pics from a D200, a D3 won't help you much. This is an award winning camera that has won more awards than ANY camera from Nikon... ever (to date).
Are there better cameras? Yes, without doubt, however, your issues, unless it is defective hardware, is not the camera, but the user. Please do not take that as criticism, just a common error with people of less experience. Been there and done that myself. The D200 is a very demanding camera. The user has to understand it and know what they are doing.
About the D700, just going by common sense, since it uses a D3 sensor and basically the same EXSPEED processor, it will have superior noise levels to the D200. The D200 is also not full frame, nor is it a $3000+ camera. Be aware that if you want the best from a D700... you will not be able to use any of your DX lenses on this camera. Figure that into the cost at the end of the day.
As for me, I know that the D700 is an AWESOME camera, but I'm already saving for a D3 and 2 lenses myself to add to my kit. If things go my way, 1-2 weeks before Christmas is when I place the order. For the cost of a D700 and battery pack, the more expensive batterys, the more expensive charger, all of a sudden you are not all that far from a D3. Add the things that the D3 has that the D700 doesn't and the fact that D3 prices will likely fall between now and Xmas, and the D700 prices will not (normal process as time passes for all Nikon cameras), and those differences slowly shift in favor of the D3. Thats why I decided to go for the D3 over the D700.