Regarding the mirror, I think what's missing is shading ( for lack of a better term) in the crevices to give it depth & interest. I'm sure others on here have techniques, but I would water down paint ( black, brown, or whatever) & apply it wiping down the raised surfaces with a clean rag, leaving some of the color in the recessed areas. If desired, you could highlight some of the decorative trim by hand with a metallic craft paint. Rustoleum makes a decorative glaze as do others, wipe off with cheesecloth.

I love your cane back chairs and the design style of these items - very similar to my taste. I recently refinished a set of 6 similarly designed cane back dining chairs and reupholstered the seat cushions as well. To provide some input on your questions, I would recommend you add some distressed elements to your mirror and chairs. In your photos, they look to be painted in white or at least a neutral cream tone. How about using some dark furniture wax to add a charcoal distressed/glazing effect on edges and in crevices of design elements. You can brush it on and wipe off as much or as little as you like. With regard to the seat cushions - yes, change the seat fabric to update with a nice natural linen and capture a new French design style !!

I used up the remaining Ben Moore wall paint (CReam color) on the chairs and mirror.

Loved your chairs. Upholstery needs to be changed though.