I think a movie that fits this perfectly is the Indian in the cupboard. Why? Because he could have used that magic key to bring ANY toy to life. What could you do? Several very profitable things.
1. Make the greatest and most affordable pets. How much does a t-Rex toy cost? 2$? How much could a mini tyrannosaur cost? 500$ 1000$? Any animal/alien/dinosaur, all available in a miniature size. Your profits would be ten-fold and above.
2. The greatest fighting sport ever. With clever camera tricks, you can make something small appear big. Something like a action figure. Something that could become the greatest cage fighter in history. Anything vs anything in a fight to the death. Low cost, low maintenance fighters, with a website to host fights, with premium content of course. Several million premium viewers would turn you into a very rich person.
So what missed oppurtunities in movies have you seen?
Edit: just to clarify I meant wasted oppurtunities by characters in movies, not by the director/producers and etc.