Your list is quite interesting, Sam. I am planning on upgrading to a Canon 40D from my current 350D, and my list of reasons for upgrading almost identically match the reasons you chose the Nikon D300 (except for being able to use Nikkor lenses, of course
).
Specifically, my reasons are:
1. Much better autofocus system.
2. Higher available ISO (3200 instead of 1600, in my case).
3. Larger LCD screen.
4. ISO setting in viewfinder. I sometimes forget to set it back.
5. True spot metering. My Rebel XT doesn't have this.
6. Better controls, especially when shooting in manual mode.
Some of the other improvements are not a big deal to me, such as the increased resolution (10mp vs. 8mp), 6.5fps and Live View. The latter feature may be of interest if I did macro shooting, but I hated trying to compose shots on a LCD screen when I used a point & shoot digital camera after spending many years with film SLRs. So, I doubt I'll ever use the Live View feature.