OP, barely any of your lenses can use the large benefit of a D700 - your 18-135, 10-20, 55-200 and 30 1.4 will all crop it to 5MP - slightly better high iso performance yes, but not a vast amount - you'd be far better off, for the 1-2 stops better high iso performance than you have at the moment, staying with your D90, or if you're really itching to spend money, a D300, and spending the rest on 2.8 glass...
and your D90 is great up to iso1600, and not even too bad at 3200, and think what specifically about 'the FF' benefits you and what you shoot, rather than just (like some people do 'IQ') seeing it as a new goal that will magically make your photos better.