Dear Miss Snark,
I have a manuscript I am about to query, and I have been researching agents. One of my dream agents doesn't appear to represent my genre (historical fiction), but she, I discovered, represents three authors, who write in very different genres, and whose work I happen to admire very much. Should I not even bother with the query or should I try it, assuming it likely won't work, but tell her I'm querying her because of authors X, Y, and Z?
The worst that can happen is you hear no and spend two stamps.
Besides, I always read query letters from people who like my authors.