I's spent almost 2 years with the D7000 and really liked it, but never loved it. I could always see the shortcomings in the images I was taking compared to what I was seeing in others' photos. Some of it was technique, but even as I fixed those things, the IQ just wasn't there. I don't make money from this, but I derive a whole lot of joy and personal satisfaction from it, much like with making music. Any investments in either of those things are meant to either stretch me to learn, or up the quality of what I'm producing.
I hadn't intended to make the switch when I did, but when Nikon did the December price drop on the D600 it was almost a no-brainer - if I'm going to make a move to boost the IQ of what I'm shooting here's a way to do it without breaking the bank considering the body was essentially $1400-1500 given the lens they were "giving away" with the kit. When I saw the results I was stunned. Everything that I'd read about cell size and its impact on quality made perfect sense because I could see it in my hand. And even with the D800, where you get a 16MP DX sensor inside you 36MP FX sensor (i.e. pixel density is about the same as a D7000) the IQ compared to the D7000 is absolutely noticeable. I believe I'm finally going to get an opportunity to shoot some examples of what I mean by that today, but it was an eye opener.
Making the move for a hobbiest means a significant personal investment, but it's not like swapping brands where everything must go, and it doesn't all have to happen at once. If you've got DX lenses, using them on a D600 at 10MP's in DX mode is going to give the average photographer photos that are so superior to what they got on their DX camera with no impact on what they do with them (you can still go 8x10 on your prints, and share to your heart's content online). So there's no need to upgrade everything all at once.
