I got off the waitlist yesterday (interviewed first week of January). I sent a letter of intent about 10 days after my waitlist notification. After viewing sdn threads over the last two cycles for this school alongside the admissions team happily accepting LOIs, I believe that LOIs have a positive effect at UIW, and at the very least, they can not hurt your app at all. I'd focus on making sure its well written and combo it with an update or any leverage you have if you can. Thank you to the people in this thread for any useful info and to those that gave up spots in case one of you donated your acceptance to me. Best of luck to you all!