What specifically do you shoot and in what conditions? As you get deeper into better lenses you will find that they become more specialized meaning if you have many types of subjects, the cost of your hobby gets pretty expensive getting lenses that are optimized for your needs. The 17-55 is a good lens, not stellar but good and well made. If you shoot what it is a good match for, it would be a good investment, provided that you are going to stick with DX for a long time. But if you plan on shifting to FX, forget the 17-55, it will suffer too much in resale compared to more in-demand lenses. If you have any desire to move to FX, stop buying DX lenses now, even if the move is a couple years from now.
Can you post am image that you think would have been noticeably better with a D7000? Depending on the weakness of the image, the upgrade could be warranted or not. No mistaking it, the D7000 is a very competent camera. I really enjoy mine but in typcial shots it is not that much different than your D5000 in image quality. If lower noise is the most important improvement you seek, a couple of speedlights and a flash workshop would probably give better results. Also, consider the 1.8 low cost primes like the 85, 50, 35 and 28 which have excellent IQ plus gather more light than the 2.8 zooms.