Definitely send an email... letters get lost in the mail and sometimes it gets read by the wrong person.
During my interview trail, I've been sending emails about once a month with updates such as academic, volunteering, researching, gainful employment, leadership positions, etc to the former director of admissions, Dr. Galindo. I made sure to express that UTSD was my top choice (it was easy since I lived in Houston...) and that the email had substance before thinking about sending an email.
I emailed Dr. Galindo in early Jan expressing my interest especially after not getting an interview from Houston pre-december 1st.... I was invited to an interview 4 hours later. My fiancee and friend got into UTSD in early March and we all interviewed on the same day, so I thought all hope was lost. So after 2 months of silence, late March came around and after throwing $2000 for my Pittsburgh deposit, I woke up one day at like 5am and drafted a last ditch effort email to Dr. Galindo stating my interests and of course included updates... Lo and behold I was offered a spot in the class 4 hours later. Persistence,
@SaeWat! I want to see you here in the fall! I'm rooting for you!