Yes - if you really want to get off the waitlist at any school, showing interest is important. However, the fact is that only a very tiny percentage ever get off the waitlist at any school. And the number who come off the waitlist is determined by how many accepted students decide to attend. So no matter how much interest a waitlisted student shows, if the school achieves its desired yield from the accepted students, the waitlisted student will not get in.
So, for everyone who is waitlisted, if this is your dream school by all means let them know. But also spend time choosing a school that accepted you where you can be happy and thrive, because that’s more than likely where you will end up.