What exactly is it that you can do with an XDK that you can't do with a modded xbox?
Spend a lot more money. While I could have gone the route of modding an Xbox into a debug unit, it still wouldn't be quite the same. One of the main limitations is that the regular Xbox only has 64MB of RAM, while the debug/dev kits have 128MB. The advantage of having an actual developer console is that I can do direct debugging through the additional ports on the back of it. Plus, I can use the recovery disks for when I screw up.
Of course, I would have screwed up a couple of consoles just trying to mod one of them properly. I can't solder worth a crap and the solder-less chips don't always work right.