I just bought the upgrade and love your plugin. Can I suggest you add another type of box as well. Your boxes are really great but there is another kind which is really good too.
Won't mention any other plugin names but a "boxes and notes" style in another shortcode plugin contains a good style.
The top part of the box is in color which has the box's title (thicker part) and a thin border of the same color is on left, right, bottom part which surrounds the content of the box. Content is in the white part, surrounded.
Any that would be awesome. Great plugin regardless.