I think you need to reconsider what you'll be doing with the camera.
My understanding of the 7D is that it would be the dogs gonads for motorsports, bird watching and similar, i.e. stuff that requires great AF AND the reach from a 1.6 crop. I'd actually be surprised if the actual image quality is massively different to what you already have.
If you don't need the AF, something like a 40D or 50D would be substantially cheaper and offer some of the functionality that's on the 7D.
If you want better IQ, IMO you really need to look at going full frame, with it's advantages of lower pixel density and DOF.
If you simply want to blow some cash, go get some good glass. IMO that would be more effective at improving the IQ that by moving to another crop camera and would also hold it's value massively better.
I know you've mentioned the 17-50, but do also consider some primes, some of which really are ace.
If I were in your position and knowing what I do now, I think I'd go with the glass. Do remember that however good the Tammy 17-50 is, it won't fit on a FF camera, meaning that if you ever upgrade in that direction, the lens will need to go.