I have tried a similar strategy with my first book (“Rosebloom” which was a IPPY award winner) with public libraries. Most libraries didn’t respond, but a few did. Sometimes it lead to visiting the library and doing a talk about the book (It was for a historical fiction book, though I’m not sure that mattered).
Was it cost/time effective?
I’m not sure. I haven’t had the time to do it again for other books I’ve since published. But it didn’t cost that much to do, it was mostly a time thing – looking up the library, trying to find the person to send the letter to… but it’s another marketing strategy to put on your ever-growing list! 🙂
Where Publishing Dreams Become Reality