Don't know about Kay; I haven't the information from anyone who has. However, most writers -- not all, but most -- love to get fan mail. Some, like Isaac Asimov, even make it a point of answering each and every one, even though that takes tons of their time (with Ike it got to where, in most cases, it was just a line or so, but he responded; this may have ceased with his final illness, I'm not sure, but I know for most of his life he answered every letter he got, unless it was abusive, etc.). I wrote to Michael Moorcock when I was about 15 and got a lovely personal response (granted, I was asking about information on one of his books, but it was a personal response). I've written to others and, in general, got such a response. These days I don't write because I know how precious time is for them; but that's no reason not to write -- just don't expect a quick answer; it may be months, if it comes at all. But I doubt it will fall on deaf ears; it will be a boost to their day, if anything.
Check with some of the writers on the forum, such as Rod or Mark or Teresa, etc., see what their take is on this. And quite a few writers have their own sites where you can e-mail them, too; so you may choose to use that route.