There are three ways to improve upon the idea of the Jack-in-the-Box.

If it were to be used traditionally as a toy, other subjects could be used in place of the silly looking clown. For girls, fairies and flowers could pop out. The box itself could be crafted out of wood, so the toy would be heavier and require more care. For boys, I would use tin or some light weight metal and have a dinosaur puppet or a spaceship come out. Boys seem to be more destructive so I would target durability to male children and sentimental value and craftsmanship towards the female. This would also vary the target age groups as well.  
Another way is to make festive decorations out of the Jack-in-the-Box. In honor of Halloween, I drew the bats, which could be made to be scary. The Jack-o-Lantern would be more on the cute side. I got the idea afterwards to make the box look like  a lantern. Jack-in-the-Lantern. The market here would be the women who spend tons of money on their holiday addictions.
The last take on the design would be to make it disposable. A Jack-in-the Box hallmark card/gift could be perfect for birthdays, graduations, new years or any other occasion.
The good thing about the Jack-in-the-Box is the diversity, which is something that has only vaguely been utilized. The decoration on the box, the music and the Jack itself can be creatively changed.