You are right. The quilt does have a lot of negative space. I find those hard to deal with. Your idea of doing a wreath or motif in the negative space, especially if you use a thread color that will show up, will make or break that quilt. For the positive space, what about loopy stars or loopy flowers. I normally don't like STID, but this may be one of those quilts that will look really good with that.
I know....I didn't help at all. Just gave you more to think about. Please let us see what you do after you decide.