Oh I adore this!!! As a letter-writer myself, I really appreciate the call to action, and I really enjoy that there's a win either way. It captures how I feel about writing letters: It's not necessarily about getting that reply back, or the equivalence of the reply, but instead it's a way to show someone I am thinking of them, and a way to spread a little bright moment in the distressing thing that is our world right now.
Plus, I stan the U.S. Postal Service, and I love any excuse to use a stamp!