It's always difficult to give advice of this sort, but given that you mainly shoot sports and wildlife, my suggestion would be that you keep the D300, wait to see what Photokina brings and if there is nothing new, buy lenses.
I have just bought a D700 as a result of the untimely death of my Fuji S5 after I managed to get rainwater in it in a freak accident and the drop in reach between a FX and DX sensor is very apparent. For my photography this is not of great importance, but it is still very noticeable.
If you don't mind me making a suggestion re a new lens, given your present list above, it would be to replace the Sigma 150 macro with the 105 micro Nikkor, I had a look at one and put a couple of shots on the card on my S5, it is a very sharp lens indeed and the VR makes handholding at a magnification of at least 1:2 in reasonable light a practicable proposition.
If at Photokina Nikon introduces a 300mm f4 with VR, use the rest of the money to buy that and a 1.4x converter.
If your main subjects are sports and wildlife, I would assume that focal length is important for you. To replicate the "reach" you currently have with your 120-300mm on the D300, you'd need a 450mm lens. This could pretty much be achieved with a 1.4x TC, but then you'd be cancelling out 1 stop of the 1-2 stops better low-light ability of the D700.
Also, from all the credible reports I have read, there isn't too much difference in AF performance between D300 and D700.
In your situation, I'm not sure I'd do anything right now.
we are going to face more difficult times. if I would be in your position, I would just keep my money and just ignore NAS. the D300 is an excellent camera and if you can exploit it to its potential, you can make quite some money with it. lets not forget - it's the skills that make the photo, the equipmen is just the tool. it's human's nature to look for excuses on the equipment side.