Why not try selling your D90 on Nikonians? Buyers and sellers here are generally really nice folks to deal with.
As for the upgrade, I'm with all others who say you won't regret it. I've had some trouble getting reliable focus out of my D7000, but I'm blaming my technique rather than the camera. I noticed when moving up from a D70 to the D90 that the higher resolution was less forgiving of sloppy shooting. The D7000 is more picky yet. But when the camera is steady on a tripod and I pick a good AF target it's spot on, so it isn't the machine that's the problem.