I was in a similar predicament a few months ago. I had the option of either buying a 24-70, or selling my D700 and putting that towards a D800.
I thought long and hard about it, but ended up going for the 24-70 on my D700, rather than the D800. I would have had a 50mm 1.4 and a Tamron 28-75 for the D800, both of which are fantastic lenses, but in the end I decided that having the 24-70 would make the most impact on my photography.
Also with regard to the comments regarding IQ, while I realise that, to an extent, MP will have an impact on quality, dismissing the D700 because it's "only 12 MP" is quite frankly ridiculous. I was editing some of my own photo's today on work's 27" iMac (um in my break of course.....

) and even at 100% on a screen that size, the quality is stunning.
Of course the D800 and D600 will give better image quality, but in my eyes, especially at the current S/H prices, the D700 is still a fantastic camera, and combined with the 24-70 is hard to beat for the money.
Would I love a D800? Of course I would, but would I give up my 24-70 to get one? Not a chance!