I keep a journal and it certainly helps. I can vouch for and agree that writing is a healthy way of getting your feelings out and sometimes helps those who don't understand, understand. I once showed my brother and parents my journal and it was eye opening.

Now, I've never written letters in the same manner you have but I would mimic what Tisha says, that if it feels healthy than by all means, but if there is serious consideration then obviously it isn't.