If you never plan to move to full frame, then the 17-55 is a great lens (DX only though.) You are more likely to see better shots with better glass than a better body.
But I know what you mean about low light (high ISO) performance. I had a D300, which was pretty decent at higher ISOs. But the D700 and D3 just kicked its butt, and then the D3S came out, and kicked everybody's butt. I rented a D3S, which was a huge mistake. I learned what I was missing, so I had to make a change. Couldn't quite swing a new D3S, but a used D3 was within reach...
I ended up selling my D300 and bought a used D3. So now I'm shooting full frame, and have a solid, usable ISO range from 200 to 6400. That and my fast glass collection, and low light stuff doesn't stand in the way anymore.
Nikkor 17-35 f2.8
Nikkor 24-70 f2.8
Nikkor 50mm f1.8D
Nikkor 70-200 VRI
The D7000 has good higher ISO performance. DXO Mark gives it a low light ISO score of 1167.http://www.dxomark.com/index.php/en/...rs/Nikon/D7000
That is quite a bit better than the D300S (787), but about half of what a D3 can do (2290.) The top of the heap is the D3S, which rates at 3253!!