Windows XP is still Windows NT 5.x, so I am not much crazier than you are. Windows 2000 is so much easier to install as there is no need to hunt down the correct VLK ISO and keys, and God forbid you want the Media Center Edition. Activation was made so you would be forced to contact Microsoft for each Windows XP and Windows Server 2003 installation, this limits the amount of installs a user is allowed.
If you're computer is best suited for Windows 2000, there are only two reasons to upgrade. Tablet PC users should definitely upgrade to Windows XP Tablet PC Edition, no surprise there, pretty obvious why. And if you want to run Virtual PC 2004, it only runs on the IA-32 version of Windows Server 2003. Virtual PC 2004 isn't really much of an upgrade from Virtual PC 5.2 anyway, and Virtual PC 5.2 does work on Windows 2000.
There isn't much reason to upgrade to Office 2003 from Office XP, and even then, the only Office 2003 component which requires Windows XP or Windows Server 2003 (due to an IE 6 requirement) is InfoPath 2003, which I don't need.