I am a prolific letter writer myself (I actually think it is an addiction - so too is collecting pens and stationery).

I admit, I don't get a lot of replies - except when I stop writing. It seems many of who I write to find exciting the act of receiving mail. The act of not returning correspondence seems more to be the fact that many people have lost the 'art' of writing than having no interest in doing so.

I think writing to someone draws them closer.

I say go ahead and do so but don't take it personally if you get no reply.