Does the letter (addressed with the paper) contribute to giving editors and editor-in-chief a good first impression of the paper? If yes, to what extent does the attached letter contribute to this impression?
I think not. If such a letter is required (many journals now support an electronic submission systems, in which accompanying letters are not assumed), then it should be just standard and polite. I also don’t think that in any journal, even one that works with potential authors by traditional methods, someone will find time to read and analyze the text of the accompanying letter. If it is impudent and boorish - then, of course, the reaction will be ...