Guess we have to have a look at the specs of the D600 and consider it worth settling for over the D800. At this point of time the price will be the big factor and as always bang for buck. Some people would be quiet happy with the lower specs of the D600 and save a $1000. But your are correct as you do have to look at the big picture at the end of the day. Once you buy a $3000 housing (presume the D600 would be roughly the same as a D800 housing) and add a body you have a D800 setup for $6000 and D600 for $5000, its only a 20% price difference between the two camera setups.
Looking at the price difference here in the UK there is currently not that much. Wex Photographic are offering the D800 at £2279 and the D600 at £1955, a difference of only £324, US$500 approx.
On this basis you have to question whether it is not better value just to move to the D800 especially if you are moving from DX to FX and you are having to fork out for new housing, lenses, ports, ext rings, etc, etc