I will try to answer some of your questions, but I want you to remember that we do not recommend specific brands here, nor do I feel confortable evaluating the usefulness of a particular feature for you.
1) 3D Color Matrix Metering II
I doubt you will see dramatic differences in real world, but I've never read any actual tests about this.
2) Bulb setting :
Doesn't look like there's a bulb.
3) On Demand GRID Lines (Viewfinder) :
I believe that's a pretty rare feature. However, focus points pattern can supplement this to some extend.
4) Is Nikons’s 11 Area focus really that much better than XSI’s 9 area Focus?
LOL! Olympus sell cameras with 3 points AF, and users are happy... This shouldn't be a real issue.
5) Nikon’s Multiple exposure
I use this often on my DSLR.
6) Depth of field preview -
It can be invaluable, if it fits your style. Both have it.
7) sRGB and Adobe RGB color space ?
I have it also, and use sRGB as most print shops around here use that. A personal choice.

multi-exposure pictures
Another personal decision.
9) Did I mention I do suck for the Top LCD option that you get with D80 but is not there in XSI ?
I would never part with mine...
Remember that you are comparing an entry-level (Canon) with a semi-pro (Nikon).
One thing that stuck me while reading your questions is that there is at least another camera that fits this list, the K20D from Pentax. I am NOT saying you should or should not select it, but since you ask for a complete picture I feel you should not limit yourself to Canon and Nikon. I own the K20D so that that into account also. again, I'm not trying to steer you away from the "big two". Remember that at the end of the day, most cameras perform extremely well. Choose a camera based on the features you want, the lenses that interest you, and above all else handle the cameras to see which feels most confortable.