I second the werewolves idea.
More after-school activities for kids and teens. Also, if and when we get a University pack, doing well at after-school activities as well as getting good grades would increase the chances of a college-bound Sim receiving scholarships and/or financial aid. On the topic of school, I wouldn't mind it if we had the option to follow our Child and Teen Sims to grade school and high school like an active career. I also wouldn't mind it if our Sims could homeschool their kids or send their kids to private school.
Battle of the Bands pack. More instruments, and Sims can be in bands for different genres of music -- rock, pop, country, classical, etc. Since we have the Kids music genre with base game and the Tween Pop genre with Kids Room Stuff, and since the kids' channel on our Sims' TVs has a show with a bunch of Sims 3 kids playing musical instruments, it would be cool if Child Sims could play in a Kids music or Tween Pop band. There could also be concert events for bands to perform at, or battle of the bands events for bands to compete in. If you have Get Famous, performing with a band and/or competing in a battle of the bands would increase your Sims' fame.