I think highly of metta, but I've always seen it as a meditation. It wasn't until a comment in this thread that I had the thought it could be seen as "devotional". I would write something about how "devotional" needs to be defined for this thread, but I think people here already over-intellectualize everything.
Reading your point about emotion and opening your heart & mind, I thought bout my local Vihara. It has a meditation session one evenin a week. It includes a small amount of devotions and ritual before & after. I appreciated it a few years ago when I had some tough times. I picked up on the emotions the people there raised in Buddhism felt and that helped me feel better. I wouldn't want devotional practices and rituals to be my main course, but thinking about those experiences I would have to agree they do have value.