Another suggestion: Maybe you can add one more stage (maybe just another "start game" option) in the next revision, which is the same as level 1 but has no "clear condition". The game should last as long as "Back" button is not pressed. It's okay to just have the 3 weapons avaliable at the start. If possible, increase the spawn rate of enemy as the game goes. Lock the total score to 9999 to avoid overflow.
The stage's sole purpose is to test out how many objects the device can hold. (So the current number of different builds and enemy troops should be shown on the screen) This is valuable information because it'll give you idea on how many "target objects" you can place when designing levels that can run on lower WP models.
Whether to take it away from the "retail" build is up to you.