The ReNuYuSenso Orb can be bought for the rock bottom cost of 6250 aspiration points and can be used by teens and older. Each one bought can be used 5 times. With this new addition, it makes changing aspirations cheap and easy, and adds a new dimension to the game. Since it is so easy to change aspirations, I have been changing Sims aspirations after major life events or when they age. When Teens age to Adults, I figure they must have learned something from their teenhood, and change their aspiration.
Of course, Maxis included a downside to using the ReNuYuSenso Orb. If a Sim is not in least at the Gold aspiration level, they won't be given the aspiration they desire. Instead they get the Grilled Cheese Aspiration. The Lifetime Want also changes (If you have "The Sims 2 University"). Be sure not to change aspirations if they are close to achieving their Lifetime Want!