Is there any way to build an ISD filter to query and return only records where a field is blank or not blank?
For string-type fields...yes, for date fields...in the works. This only works in the Filter box at the bottom of the query panel, not in the Filter Builder, To return string-type fields that are blank, enter < ! and to return those that are not blank > ! Note that there is a space between the arrow signs and the exclamation point. So to return only those records where FieldA is blank, you would right-click on FieldA in the query fields list and select Add to Filter. Then go to the right of that field in the filter box, below Value, and type in < !
