Welcome to the forum.
Do you routinely make large prints? If not, then upgrading just for the sake of more mega pixels would not be my recommendation. The image quality of the Digital Rebel is good enough for most applications.
On the other hand, there have been many other improvements. The newer cameras have a faster frame rate (good for sports, actions), the 30D is quite fast. The autofocus of the newer ones is probably faster than your Rebel. The electronics are better which gives you a bigger buffer, less digital noise and a much faster start-up.
The Rebel XT is a fair bit smaller and lighter...but the 30D has the great thumb wheel on the back. The 30D has a bigger and better LCD screen, spot metering and other improvements.
The 30D has a stronger body with more metal, while the Rebel cameras have more plastic...although they are not toy-like.
If you can get into a store and try them out...do it. The Rebel XT is too small for some people while the 30D may be too big and heavy.
You may find that your money is better spend on a new lens, have you considered that?