I most wish for........ spot metering.
I really doubt that they'll do that. They used to only provide spot metering on their 1D series. With the last round (30D and 5D) they've included a slightly wider (3.5% vs 2.4%) spot meter on their mid-range cameras. I doubt that they'll ever put it on the Rebel series. It's one of those things they use as a differentiating factor to entice people to buy further up the product line. You do still get partial metering (like spot metering with a large spot).
As far as the differences between the XT and the XTi, here is a quick list:
1) Higher resolution sensor
2) Automated sensor cleaning system
3) Better autofocus (uses the 30D 9-point system)
4) Can take more shots before it slows down to write to memory card (RAW went from 4 to 10, JPG went from 14 to 27).
5) Larger, brighter monitor LCD that combines the functions of the monitor LCD and the status LCD. The status LCD is gone.
6) LCD turns off when you look through the viewfinder
7) Selectable parameter groupings called "picture styles"
8) An updated menu interface
9) Histogram can be displayed as RGB instead of just brightness
10) Up to 9,999 images in a folder instead of just 100
11) You no longer have to press "set" after making changes
12) Some new direct print features
Of those, I (my personal opinion) think that the important ones are #3, #4, #9, and #2. Most people will dwell on #1, but you're only going from 3,456x2,304 to 3,888x2,592.
I think the improvements in the AF will be of enormous help to people shooting kids. The old Rebel's AF was one of it's biggest sources of complaints.
The bigger buffer will rarely be used by most people, but when you need it, it's critical. I typically need the extra buffer when my subject is doing a brief routine of some type (skating competition, gymnastics competition, Tae Kwon Do bout, etc.). In those cases I find myself taking a huge number of pictures in a very short period of time.
The RGB historgram comes in handy when you are shooting very saturated colors. With my 60D, I would sometimes carefully check my histogram while shooting flowers and then get really frustrated to find out later that while my B&W histogram looked good, I had been blowing out my red channel.
Time will tell how useful the dust shaker is. I'm certainly hoping that it helps a lot and becomes standard on all new models.