Granted and your initial points are all valid. I think its just a case of wanting to do everything within your power to help persuade the school, but one's expectations shouldn't be significantly raised by writing one.
I sent a letter of Intent to one school I really want to attend. My application is strong and my stats are well above that school's averages, but I didn't hear back from them. I had no illusions when I wrote the letter to them and I expected nothing much to come out of it. I still haven't heard from them and I don't much care anymore, but at the time, sending that letter of intent put my mind at ease. What I am trying to say is the LOI was more placebo than cure for one's admissions woes - write one to feel you've done the most you can, but don't think it'll magically make things better.
