Mehhh, while I always like getting a new world, I'm always instantly irritated by how TS4 does it.
They give us a nice big world and 70% of the world is nothing but set dressing and backdrops taking up precious real estate space that we can't actually change. Even though I would really like another world with many more lots, I hate that I am forced to make my houses/lots match the world's style (because I have to have things aesthetically cohesive and match the environment around it).
Like for example, I can't place a bunch of retro/mid-century modern houses down in Windenburg without them looking glaringly out of place.
That sets my irritation level to 11 every time I have an idea of changing/creating my own world.
So buying just a "world pack" with objects/CAS items that didn't offer any gameplay elements to somewhat appease the annoyance of not having the ability to change/edit the world as I want, would not be something I'd be interested in.