I sew my miters closed so little fingers do not start picking and make a mess of the miters.

This is a great question, glad you brought it up. So far, the quilts I have finished either have no borders or have corner squares, so it really hasn't been an issue for me. I think it also depends on the fabric you are using. For example, does the border fabric have a large print or is it a solid that kind of blends into the background. I am making a challenge quilt for a show in 2018 with solid borders and was wondering if they really needed to be mitered.