Well, this makes me think and also makes me wonder if I should or shouldn't get it... If you don't see a difference between the 600 and 800 shots, then I probably won't... And I've already had written and thought that I did NOT need the extra definition and file size... Ah man, why is it so tempting then.. If only I was poor and didn't have the money the question wouldn't even be asked.
I have looked in the past into the D800 / D800E. Sometimes the urge comes back as future machine, but it does not seem for me at the end.
1) I do believe that the D800(E) is an upgrade from a D600, in control and functionality, e.g. AF system
2) Extra definition goes for D800E but it seems to be only for freaks on definition, since you are not into it it would be more D800 it seems for you. I was more thinking about every hair on insects in macro and would think about D800E.
3) Extra definition on D800(E) also will make you look at better lenses and will require a lot of attention to technique. It is a game changer, the sensor is capable of getting the best out of the lenses, which was uncommon before. More definition also requires better technique to get the maximum out of the machine.
Look at the shots you like to take and only afterwards what the D800(E) would add to that to see if it would help you. Obviously other possibilities might change the way you look at photography, that is something to consider as well.