You're doing all that Kevin, and you think I have the magic bullet? I think I just found my future PR consultant.
Most of the stuff I know about PR -- and it's more limited than I would like --comes from authors I know who've tried various things. My pal, Diane Mott Davidson, who does culinary mysteries about a caterer sleuth, was pretty brilliant at this, though the market has changed a good bit since she started back in the late eighties. She had a foot-in-the-door deal with St. Martin's, no promotion, in a very crowded but then hot mystery market (kind of like fantasy today.) There was a whole network of mystery specialty bookstores then, gone now along with most of the sff specialty bookstores, and it was just the beginning of the superstore movement, so there were more independent stores too. Here are some of the things Diane did for her first and next couple of mysteries that may or may not be effective today:
1. Postcards: She did a postcard with the cover art on one side and book info on the other, and mailed them to every mystery bookstore and a bunch of indepedents and such. This let them know that her book was out, in case they hadn't heard it from the publisher, and even if they tossed it, it would make the cover art familiar-looking.
2. Food bribes: Part of her mysteries are recipes that Diane concocts herself and which contain clues to the mystery. In the first one, there was a great recipe for cookies and another for brownies. She shipped batches of these baked goods to mystery bookstores with a letter introducing herself. She also took them to every signing and every conference, convention or related event she went to.
3. Swag: Diane also did the bookmarks, some T-shirts, refrigerator magnets, napkins (to go with the baked goods,) and the like, all with cover art. She didn't do tons and tons of them except for the bookmarks, napkins and postcards, but she did have them on-hand, gave them as bribes to booksellers, etc. A lot of other authors have done this, and while I have no evidence that it has great effect, it doesn't seem to hurt either.
4. Touring: Diane teamed up with three other better-known mystery writers and they did a very carefully planned circuit of California as the Lethal Ladies on Tour. They hit mostly independent and mystery specialty bookstores. Her publisher was so impressed by this that they coughed up some money to help with her expenses.
Teaming up with other authors and doing an event, in a bookstore or elsewhere may be effective, at least to get your name out there. Bookstores are usually more interested in a group of authors than a sole person. Independents may be better bets than the chains, who vary widely by store and region. (In Lubbock, Texas where I lived, the Barnes & Noble supperstore was about the only bookstore in town and so did lots of stuff with local authors. But the superstore I live near now doesn't seem to do as much.) Doing all the local and regional stores you can, at least introducing yourself to them if not a signing or reading, as you've been doing, is generally a good idea.
5. Conferences and conventions -- there simply aren't as many of these for mystery writers, as for sff, but Diane also did writers conferences. You as well, Caitlin, would be able to do contemporary/literary events and conferences, plus there is the sff convention network. There are also related conventions -- comics, film & t.v. that draw sff authors and fans too.
Gary Wassner, who works in the fashion industry, got press with fashion media about his writing. You may be able to do something like that with other areas of your life which have their own networks, for coverage, reviews or just announcements.
Here are other things I've heard -- don't know how effective they are or are now:
Find out when vendors and wholesalers will be placing orders. Do a mailing announcing the release of your book around that time to distributors, wholesalers, jobbers and bookstores around the country. (Note: there are many fewer of these than there used to be. Jobbers supply non-bookstore venues and have decreased in number, and the wholesale market in the States has been pretty much taken over by Ingrams.)
When the book is out, do a second mailing to people you know or have met at conferences, autograph parties, who've sent you fan mail, in classes you've taught, store clerks, bank tellers, parents of your kids' friends, high school pals, and anyone who's expressed any interest in your books.
Arrange to buy a batch of your books from your publisher at a vendor's discount (near cost) and then you can sell them at events and such. This is a favorite of nf writers who do seminars and workshops and speaking events and sell their books at them. Fiction writers may be able to do it on a more limited basis. Greg Bear, a major sf writer (one of the three Greg's,) was known to sell copies of his books from the trunk of his car at sf conventions.
Contact your local librarians and offer to do a speaking appearance as part of their library programs. This is a favorite tactic of children's authors. Libraries usually like to encourage local authors.
Library Association conferences or bookseller conventions like Book Expo in the States might be useful to attend and introduce yourself to librarians and booksellers (and give them the free swag.)
If you have a specific publicist assigned to you at Penguin, you'll want to talk to them about things you can do. They're probably not doing anything on you right now, but if they have any bound galleys of Silences lying around, they might be willing to give them to you and you could try to get some more Web reviewers interested.
I don't know that I'd try doing all of this. I agree that it's like exercise, and it's very hard to tell if it's working. The big goal is to get your name out there -- to booksellers and suppliers, to die-hard fans, to more casual fans, and to non-fans who may be interested. You can use your magic-realism-related lit-cred, Caitlin, to do stuff in that market, with those web-sites and the like, which can help increase your audience.
I don't know if blogs are a big deal or not, but if you tried one, you wouldn't have to put in an entry every day. You could try it once a week, or something. I suspect blogs are more useful for muscians to tell stories from the road for fans, but I do know that actor Bruce Campbell kept a log of his booktour adventures on his website and then put those into the paperback version of his memoir. (Which was annoying, because we'd bought the hardcover.)