Although you say that you're not looking for the best of the best, the D7000 is just that - image-wise (DX), anyway. It performs exceptionally well at higher ISOs, has an excellent focusing system, wonderful ergonomics, a screw-driven motor for AF-D lenses, and can control Nikon's CLS. What more could you ask for?
My suggestion is this: Pick up a used D7000 and shoot with it a while. I regularly see them selling for $750. That will reduce your budget to about $450. After you shoot with it a while, you can sell your D90, add the proceeds to your original budget remainder, and pick up a backup D7000.