Just re-reading this thread and was struck by Barmaglot's comment on 22 January:
I moved back from a full-frame D800 to the D500. In terms of image quality, can you really improve significantly on what the D500 can produce? What realistically does it lack? Yeah, maybe there have been improvements to AF but, really, does it make that much difference? And it terms of size of system, all the various, impressive, studies I have seen people pull together, the relative difference when you add on all the bits, bobs and dooh-dahds is minimal.
Yeah, if money is no object and you fancy a new system, go for it! But in terms of the images you will create,, are you really going to do better than you can can with the D500?
Like Chip, I love helping people spend their money on this stuff: it's a guilt-free pleasure. But on this occasion.... hmmmm... spend it on a trip to take images. Two or three trips possibly!