Get to Work's main feature was active careers, but in later packs we've had other active and semi-active careers, including the most recent acting career. There are also many small features locked to older expansions, like new club requirements or events going into the calendar. There are also examples of similar features that don't overlap, like retail, restaurants, and vet clinics.
We also have the question of how much similarities we are OK with between expansions. Showtime is the best example of where it has so much similarities to Late Night that it should have been in the previous one. Conversely, Late Night also has an example of how repeating certain content can be a good thing, as the poor iteration of vampires were much improved with Supernatural.
So really it's a matter of how unique a feature is, the twist that makes it different from previous games. It could be differences in how the feature works, or just having a different environment or style.
