I think too much is a little silly. But I see no issue with a few judiciously placed small crystals on the tack to catch the light and draw the eye to the shape and movement of the horse. I love how a conservatively ornamented browband looks on a perfectly turned out horse. Everything should enhance the beauty of the horse. I dislike grey jackets for that reason. They always look ill-fitted and cheap to my eye, no matter how expensive. A blue jacket coordinates better with bays than a black jacket. Otoh, I dislike anything but a black jacket with a black horse.
Dressage has a special formality due to it’s military roots. Military dress uniforms are perfectly fitted and eye-catching in their ornamentation. They’re symbolic of strength and discipline. A little bit of the same translated into modern dressage isn’t a bad thing in my book.