I think a whack-a-mole game sounds fun, and I think robotics is a definite interest for some kids at least, plus it grounds them for the future. I was thinking that they would learn both programming and electronics basics; for some standards at least, there is a need to use inputs and outputs in a program to create a working project. However, I concede that this is not the most fun project for kids.
The Arduino C++ is a fantastic language to begin with, plus its compatibility with many libraries. I definitely think it could be used more in educational settings.
Maybe this is a better project for an after school program than a class setting, or any spin-offs. Any feedback from educators would be greatly appreciated!