Somewhere along the line, I think it was probably in junior
high school, we learned that like poles of magnets repel each other and that opposite poles attract. Then somewhere else along the line, we promptly forgot that lesson. Especially when it comes to designing our homes.
How many times have you seen a collection of similar things on display in a room? Perhaps even in your own room? Generally what we have here is a shrine to the ability of the designer to identify like qualities in things and group them together in one place. And while that's certainly a skill, the result is less than appealing to our senses. In fact, the result is almost always boring.
What we need to do with things that have like qualities is separate them throughout the room with things that have opposite qualities.
If your wallpaper is of medium contrast with smallish sized elements, then a display of medium contrast things that are smallish sized themselves will get lost. Your display of objects needs to have contrast to the wallpaper in size, coloration, shape, texture, or several or all of these.
What should coordinate these objects is their intellectual relationship (reading glasses and pieces of marble resting on a book about rock collecting), not merely their physical similarities. Intellectual coordination is improved by contrasting physical similarities within the arrangement.