I think it makes sense to buy more Nikon equipment and you've got great lenses to boot.
I was also going to recommend keeping the D70 for macro and for when you need extra reach with the 70-200 with or without the 1.4x. But the DX crop of the D700 will basically be the same megapixels as the D70.
SteveK My Nikonians gallery 'A camera is an instrument that teaches people how to see without a camera.' -- Dorothea Lange