Thank you for your opinions, everyone. Yes, Stan, I will hold on to my family, hehe.
Having thought about it further, I think that at this stage D600 is definitely more of a "want" than a "need". Especially since I have not actually spent much time using my new FX lenses on my D90 to see how the quality will improve as compared to my previous lenses. As a consequence, it may be prudent for now to stick with D90 and see how my new lenses will perform - I might be perfectly satisfied with the results.
As such, the money would probably be better spent on getting a better tripod(I understand that my Manfrotto 190PRO will not be able to handle 24-70mm and especially 70-200mm).
One dilemma which I will face if I stick with my D90 is what super-wide lens to buy (which is a lens I am currently lacking). I would want to complete the Holy Trinity by buying 14-24mm, but I understand that it is not that wide on DX. At the same time, I am a bit hesitatnt buying a DX lens, in case I will move to FX camera in the future...
Oh, those pleasant Nikon ownership and NAS problems!