Generally, buyers are more impressed with how much usable living space they have, rather than the number of rooms. Knocking down a wall will help create a bright, open-plan space and give you one impressive room, like this light-filled Furniture And Choice scene, rather than two underwhelming ones, while also adding to the home's value.
However, make sure not to get rid of all the walls in the living space. Some closed-off spaces, such as hallways and homeworking areas are desirable, so a broken plan layout may be the best of both worlds.