Did I miss it or did the OP never say what kind of photography he is interested in? I know he just mentioned the 1600 ISO limit. I would agree in your case a body upgrade might make the most sense. I always suggest buying a generation behind when you are on a tight budget so a D7000 refurb and some better glass would probably be the best upgrade, imho. of course depending on what you shoot?
Right now I kind of do a bunch. Landscape, portrait, astrophotography, sports.
thanks for all the replies everyone! Really appreciate it.
One last thing, I know some people recommended just getting the d7000, but would I really be better off buying that, or spending the extra money and getting the d7100 which is up to date?