Mine have consisted of 'here's why I'm writing to you. Here's what I've done since my interview and/or last update (7 publications). Here's how I fit your mission statement. Here's why I love your school. I'd love to join the class of 2020, blah, blah, blah...'
That seemed to be the general consensus in the other threads about letters of intent. With that being said, I'm still on the wait list. While I've got another acceptance, it's DO, and I'm pretty sure that doesn't carry much bargaining weight....