For those who want to change the default printing DPI for your WAB print widget I have found the spot.
This is for the Developers version
in \widgets\Print\templates\Print.html line 143
change the value:300 to the desired dpi value
<input type="text" data-dojo-type="dijit/form/NumberTextBox" data-dojo-props="name:'dpi',required:true,value:300,style:'width:100px;'"
