I think a small mirror would be nice. Just for fun what about installing beadboard or tongue and groove on the white half-wall thing and make a decorative wainscot?

I would put a full size 24 or 36 inch wide mirrored medicine cabinet over the sink. Then the towel bar on the left wall and the wastebasket to the right where it can be shared with the laundry machines for lint, tags and so on.

Alternatively, move the sink toward the window a few inches and use the left wall for a long or short closet rod to hang laundry that has just come out of the dryer or that you want to drip dry. The towel bar would go under the window. Having an extra towel bar near the washer for damp things waiting to be washed is quite useful.