The 30D is worth it, in my opinion. The handling of the 30D is different, and much more pleasant in my opinion (I briefly owned an XTi but found it too small for my hands to be comfortable with it). For instance, the 30D has a dial on the back which allows you to adjust the shutter speed and the aperture independently and quickly, while the XTi requires that you press a button while moving the front dial in order to adjust aperture (while in manual mode).
The 30D's autofocus is reportedly better, but I never got a chance to use them side by side for comparison.
The 30D has spot metering, which I find very useful (makes it a lot easier to do moon shots, for instance).
And finally, there's a world of difference in build between the two, with the advantage going to the 30D.
If the prices are anywhere close, I'd go for the 30D.
Note, too, that with the advent of the 40D, you should be able to pick up a 30D on the used market for a very good price. Check the classified forums here on POTN.