In your blog, you briefly touch on the topic of overdone subjects/storylines, and as a reader, I can completely agree that just because you call a chocolate cake 'better than sex cake' does not change the fact that it is still simply a chocolate cake with whipped cream topping. Regardless of the name, it will still taste the same. Now, as a writer, my thoughts on the subject are slightly different.
My question is: If, like myself, a writer finds their 'genius' pointing them in the direction of a redundant topic, *cough* werewolf, how can they be sure that their story is original enough to stand out? Also, as a literary agent if you were to read a query for a story, such as my own, would you automatically stop reading it the moment you realized what it was?
You've certainly given the right example. When my urban fantasy colleagues howl about shopworn topics, werewolves and vampires lead the list. It's very hard to get their attention for novels with either.
When you elect to enter the world of trade publishing, you've essentially signed up for people to ask "why should I pay for this book." It's not enough that it's good, or a good story, it has to stand out from books they already own or have read.
I like to think of this the way I think of meatloaf.
I really like meatloaf. I make it using the recipe on the back of the Quaker Oats box. I may change a few things, but it's essentially the same as what millions of other meatloaf lovers are making.
Were I to open the Shark Cafe (ie enter the world of trade cooking) and serve meatloaf, how would I personalize it so that a customer bellying up to the counter and ordering meatloaf would not say "hey, this is exactly like the recipe on the Quaker Oats box!"
Even though I like that recipe a lot, I need to personalize it to make it my own.
And that's what you have to do with werewolves and vampires, and alcoholic ex-detectives, or soon to be ex-detectives, or down and out lawyers, or sinister billionaires plotting world domination, or any of the other characters that have been around a long time.
A great example of putting your own spin on both werewolves and vampires is Dana Cameron's Fangoborn series. This started out as the short story The Night Things Changed (nominated for an Edgar!)
Charlaine Harris and Stephanie Meyer both added their own individual twist to paranormal tropes to make them distinct.
The answer to your question of how to be sure your query is original enough to stand out is two-fold: first you've got to be so well-read in the genre that you know what everyone else is doing. Second: you have to show me you're different by what you write in your query. Just say "werewolves and vampires" and we're done. Say "werewolves and vampires are all part of the Fangborn family" and you've intrigued me to read more.
As for when I stop reading: if the writing entices me, I keep reading. There are lots of very good books that described simply in terms of their "ingredients" wouldn't sound all that special, but the writing livens things up a lot. In other words, give me a forkful of meatloaf, not the recipe.