I sold my 35mm f/1.8, my 10-24mm and my D300 to partially fund my D600. (Well, still haven't listed my D300). Couldn't be happier, but haven't checked mine at small apertures for dust yet. The dust/oil issue is the only negative I can think of at the moment for me. No aperture change in live view for video is apparently an issue for some, but not for me.
Going from the D300 to the D600 was primarily driven by my constant shooting indoors with no flash. The D600 is light-years ahead in the high-ISO department for me.