Good comments. I've got a D7000 and am totally happy with it. I went to the camera store and tried the D7100 because I was interested in better viewfinder icons and a sharper LCD screen. Nothing more. Don't care about the extra megapixels and other refinements.
I was in surgery and released from rehab yesterday. In the time I was a prisoner of the health industry, it seems news of an impending D400 over-rides most of the arguments about the D7100 advantages.
Do I understand that correctly? Keeping in mind that I'd have to sell my D7000, and want to keep my DX lenses (4 of them). And I really appreciate light weight and compactness.