Haven't seen them but let me know if these are already in the game:

Deluxe walls and ceilings that have elements of animation or clever 3d.

For example:

Ceiling that appears to be the sky outside, like you see in Harry Potter. (Walls able to do this too). If having it change to the time of day is too much, they can be permantly one time of day (or have a pre-set animation cycle).

Waterfall walls or at least features that can socket into one wall (not needed to replace all walls lol).

Space, such that a room appears to be vast. (Outerspace)

Windows that open up to vistas, like the one that is seen in Merlwyb's room (which of course isn't a fully rendered vista just clever image placement)



Also other items like:

Special effects, perhaps from powerful crystals. For example a water crystal that makes the FC floor appear to be covered in water (stairs have water coming down them). Weaker water cystal could do just the bottom floor, while the stronger one affects all floors. Another could be flowers/grass on the ground, and fireflies in the air.

This flower patch: