I press open too, when it's required to make certain seams look flatter, and I've never had a problem with it. I do use a small stitch length and stretchy polyester threads and have never had my stitches pop.
Closer quilting will generally strengthen a quilt. You want to make sure that the quilting is consistent or you'll have some unevenness to your quilt. I have been watching a show on thread painting by Terry White, and she densely paints in places, and then creates what she calls "environmental debris," which are little tack-downs around her quilt to help balance out the more densely quilted places so they don't look "warped". But in general if you commit to dense quilting, you should make sure it's balanced throughout the quilt.