I dont think I see myself parting from any one of my 4 xbox's. I barely even use my 360 the way it is now and I use XBMC all the time on all of the original ones. I plan on picking up even more after an assumed pricedrop. I see the fun that can be had from the original console is endless with all the things you can do. I cant wait until I get XBMC running on every tv I have in my house, including the one in my bathrooms (see sig-link).
Until the 360 can not only become as good as a media center as XBMC but can also play snes, nes, etc roms and run linux and all the other fun stuff I dont see any reason to stop using the "old" console. Even then, I would much rather pay ~$50 per xbox (ebay) as apposed to the $400 per 360. But, I cant complain, I paid $0 for my 360 (thank you mountain dew!) and I do enjoy it but at the same time I feel much needs to be done with it.