Nah, you don't need to up the wattage. In fact, that is a bad idea. You can't just replace the standard PSU with, say, a PC one, because they will cook your mobo.
Unless you are just like... I dunno, hooking up a toaster and stove to your stock PSU, you have no need to upgrade it. (Slight exaggeration

) Take a look at
Gavster's XBox. A picture of his XBox is about 3/5th of the way down the page. If he doesn't need an upgraded PSU, none of us do.
If, however, you put so many LEDs on your XBox to warrent more power... you have more spare time then all of us combined!

Good luck on your future projects.
- Greg