Good idea for a post - there are no easy answers here. I have to disagree with some points, but this is a time when it's probably easier to decide if you've got the right gear as opposed to the time when you replace a film SLR. I say this because all of your lenses (at least those of us with smaller-sized sensor DSLR's) have now changed their effective length.

With a Nikon system, you can get the 12-24 DX lens for about a grand. Sure, the 80-200 f2.8 basically gives you a 300 f2.8 but you lose the wide end. Add another thousand to the package if it's something you need. This will be true of both Nikon and Canon, one (expensive) full frame sensor camera available per brand. I'm sure Canon has or will have a wide zoom like this, the 17mm or 20mm just isn't that wide anymore on a DSLR.

Other things to consider if you switch brands - all of the accessories that accumulate, like flashes and electronic cable releases. However, they may or may not be compatible to some extent with a DSLR. There's also the lingo, Nikon calls it matrix, Canon calls it evaluative. I suppose they handle differently too but I don't have experience with Canon. All of the recent Nikons seem to handle pretty similarly. If you change brands, you've got to learn more about how the new camera works. All just part of a big learning curve.