There's SO much more to the GBA port of Super Mario Bros. 3 than just e-Reader Levels. The e-Reader can do a LOT more.
The Switch Cards allow you to modify physics and behavior in the Main Game & World-e, and Power-Up Cards let you get otherwise unobtainable items, such as the Cape Feather and Boomerang.
https://youtu.be/2o5JJiANsHQ
The video above links a pack of save files in the description so you can play the main game and World-e with these enhancements from the e-Reader Switches, as well as a full inventory of the items that you cannot get except by scanning the e-Reader cards.