...are there other benefits in image quality to justify 5 grand?[a href=\"index.php?act=findpost&pid=226054\"][{POST_SNAPBACK}][/a]
"Other" benefits than what? Although I can think of several image quality benefits, you haven't specified what they are. Whatever the benefits are, you are the only one who can determine what the value of those benefits are. Just to clarify here, what you really want to know is if the difference between spending $4500 over $2500 is worth it; and the answer really depends on what you are going to do and how much money you have.
I think you are proposing an "all or nothing" proposition. Consider instead that you are comparing different camera bodies, different lenses (one of which is a stop faster), and even different fields of view at the narrow and wide ends. Each one of those factors favors the more expensive option you proposed, and the price difference should be parsed between all three as well as the improved image quality which will be more obvious when comparing the D700 and Nikkor 14-24/2.8 at 18mm to the D2x and 12-24/4 at 12mm. I think with the D2x and 12-24/4 at 16mm and stopped down to f/11, you would have a hard time justifying the $2000 difference.
The question for you is: What are you trying to photograph and how much do you need to spend (or are willing to spend) to accomplish that? For better higher ISO capability you will spend an additional $1500 on the D700, for faster lens speed and better IQ you will spend an additional $1500 on the Nikkor 14-24/2.8. For all of that and the wider field of view you have to spend the extra $2000.