Strictly speaking, you don't add magical bonuses to miss damage. This isn't spelled out in the rules directly, but in one of the magical items (the Victory By Inches belt on page 288) which has the property of allowing you to add that magic bonus to miss damage. If every magic weapon added to miss damage, that would make that item completely useless.
Currently we're discussing this same subject over on G+. It seems split about 50/50 of the opinion that magic weapon plusses do not count towards Miss damage.
https://plus.google.com/106448418478953764803/posts/8V7EEe8inpp
I side with +Aaron R: