Friends stay friends in part because they find each other interesting, even amusing. Likewise, boring appeals never raise money.
Your donors should come to expect something fascinating every time they receive a piece of mail from you. A letter to a donor should have life. Pep. Zing. Or drama. Or charm. Or bits and pieces of all of the above.
If the donor comes to expect boring, low-energy communication from you mailing after mailing, the relationship is doomed. Your donors, just like virtually all the Christian donors in the marketplace, need their interest to be gained and held.