I have both, and I think you have figured it all out. The loss of the extra bit is a big deal. Plus, the scissors on the XT are pretty ridiculous. They are about 2/3 the size of the ones in the old wave and difficult to use.
The cutting hook comes in handier then I would have imagined. I sharpened mine up so that is easily cuts paper. Great for opening boxes, for cutting paper, for cutting strings/lines, cloth, etc... It could use a good sharpening however, as it comes out of the box.
So, between the hook and a sharp knife blade, there are very few things I can't do with the those two blades that I needed a scissors for before. Certainly more useful than the stunted pair they give you in the new Wave and the XT.
Then you can really multiply the utility of the XTi, more so than the XT, because of the two changeable driver sockets if you buy the extra bit kit. I would view this a required equipment for an XTi.
Get the XTi and return the XT and buy the extra bit kit.
J.