I've created Version 5 of the app with Levels based on data. Data was the last part of Vizwik that was not being used in the game. With a Data editor you can define both the sprites, backgrounds, and messages displayed in the dialogs on collision. This is done using tables that have rows that map to the level you're in, and loaded as you enter each level. The students can look at this data and figure out how to add new sprites and new levels. I've added 2 as an example. 

I also limited the number of different kinds of sprites to 3 on any level. You'd have to change the data and the New Sprite script to change this.

Adding new levels also means testing for the last level which means changing the Next Level script.