The only problems I see here are the things you mentioned. The art over the toilet is too small. Wall color is too dark. By "fixtures" do you mean the faucet & towel ring or the sconce light fixture? I think the sconce light is too traditional for the space. I would go with a more contemporary light in a finish to match your faucet. Is the faucet oil rubbed bronze or flat black?

Other than, the bathroom is beautiful. I love the vanity, faucet, floors. Just those 3 quick fixes and I think you're done

Lighting above mirror, maybe remove some mirror or get new.

If you want to add character, maybe an accent wall? Two different complimentary tones of the same color would keep it from being too busy. Or maybe wood moulding on the bottom half of the wall if you want a more classic look

I think ceiling is arched or beveled I wouldn't do that.

I see that now. You're right, happy leg, nix the moulding.

Thanks for the comments. The fixtures are rubbed bronze. Any advice on a better sconce? I should have mentioned that the bathroom is under the stairs so that is why the ceiling is looking beveled.

Sconces

Does the vanity/mirror go all the way into the corner? If not, I definitely would get that area wired to put a small light on both sides of the mirror over the vanity. Or even wire an overhead light for the vanity area. That should be enough lighting for the whole powder room without changing the wall color if you want to keep it.

The mirror does go all the way to the corner and to the ceiling. So would have to change the mirror to get more light. Not sure I want to do that as the larger mirror helps make the room look larger. However changing the sconce will be a challenge as I need something that gives off a lot of light since there really are limited options for adding more lighting.

I actually think the current sconce is pretty cool, and I like the wall color; it's nice and dramatic. How much light do you need in a powder room anyway? Enough to find the toilet paper and check if you have spinach in your teeth. The only thing I'd change is the picture, though I might frame the mirror in something that goes with the current sconce.

Oh, and I'd hide the toilet brush.

Love #1 & the purple!

Is that Klimt, groveraxle? Perfect feel with the light fixture.

Yes, DH, it's Klimt. I was gonna do Mucha, but thought it would be a little mucha. ;-)

I seen a Raspberry bathroom that was stunning!

Yes a longer picture. But I'd try a stencil design on the horizontal part [upper also idk], using paint that's on the walls. If suited to sconce, etc... could be nice.

Maybe this? I don't know what they look like in person.