I already posses a d700 and a d800, both very sparingly used by me. One brand new d700 is available with 2years Nikon warrenty. I am extremely happy with both of my cameras, however D700 will not be available in future if needed. May I go for the above stated brand new d700? I have to make an urgent dicision.
Do you actually have a use for a third camera body? You have two great cameras and each can act as a backup for the other (even though they have somewhat different specifications). The fact that new, warranted D700's may not be available in the future also applies to all other camera models that have been out for a while. Do you feel a need to get a D300s, D90, D5100, or some other model? These cameras also will be unavailable (as new with warranty) sometime in the not-to-distant future.
Since you are asking this question I suspect that you have not settled in your own mind why you should purchase another D700. If you want it, and you can afford it, then buy it and enjoy it. If you or somebody else would have to give up something to be able to purchase the new camera, then you must make a decision about which is more important: The camera, or the "something else."
If you currently use your D700 and D800 sparingly, why do you feel the need to add a second D700 to your kit. I guess it depends on how you discribe "sparingly" and your future plans. As Brian wrote above, only you know what your personal requirements are, and therefore only you can answer that question.
I faced a similar decision. I had a D700 and (at the time) D7000. Knowing that the D700 was discontinued, I chose to pick up a second body. I did so because the D700 is all the camera I will need to do what I want to do. Also, I didn't want the larger files of the subsequent models. But the biggest reason was that I felt more comfortable with the D700 than with any camera I've ever used.
If any of this seems familiar to you, go for it. But, as was mentioned above, if you don't need it or are just buying to be buying, you might reconsider.