Do you think that spam letters are generally considered to be a good use of resources?

No, but it counters this point "a letter would involve actual emotion and thought and be a dialog between two humans."

I don't think it does unless you ignore the context of the conversation. Its very clear that the reference about "letters" being made wasn't "all mail."

Writing personal letters has other dangers as well. Remember how George Costanza's fiancée got killed.