I am not a fan of Yachtsman, although DBF is. We celebrated a birthday there once. My steak had a large piece of grizzle running down the middle, and the table right next to us was 2 families with young children, who, at 9 PM were understandably tired and cranky. The parents were tired and cranky, and we could hardly hear ourselves think. When a deluge opened up on us on our way back to the Poly, I took it as an omen.
As to dressing for signatures...I usually wear a summery dress or dressy pant outfit because that's what I like to do on vacation. But, I think you will be OK in most anything short of shorts, although the one time we tried Bistro de Paris, there was a family there in shorts. Cause it's Disney and you can't ever tell what you're going to see!