There are many benefits the D700 has over the D7000, like a much larger view finder, more solid handling with more dedicated buttons and switches, and the ability to use fast primes like the 24mm f/1.4 at their full field of view. These are all indispensable to me but may not be to you. Image quality will probably be close. FX is generally superior at similar MP count, but the D7000 sensor is 3 years younger than the D700/D3 sensor.
Why are you upgrading from the D5000? If there are features you are missing, that will point you to the right upgrade path. Example: If you are mainly missing the focus motor to operate AF-D lenses, then the D7000 will be a perfect fit. If you don't know why to upgrade and just want a better and more capable camera, again take the D7000.
So I think the answer won't be all that hard. If you needed something that only the D700 provides, I think you'd already know and wouldn't need to wonder.