The answer was something to the effect that a writer should keep querying until he/she either sells the book, or until the next book is finished. The assumption, I gathered, is that when the second one is ready, you've probably grown in your craft and the second may just sell first. If so, then the first book might be also taken more seriously and might sell as well. But those could be a BIG MIGHTs!
I also read that if you've sent out 20 or so queries without any requests for partials or fulls, you should consider re-working your query. It's obviously not catching the agents'/editors' attention. However, I can't help wondering in my case, if instead of it being the query letter could it be the subject matter? I mean, after all, my first novel is a young adult novel, set in 1965 during the Vietnam War. I call it a YA historical suspense. But how many agents/editors are interested in that genre?
So, now that the economy is bottoming out, I'm toying with whether I should resume querying, and if I do, should I keep re-working my query (I'm only on the umpteenth version now), or assume agents/editors just are not interested in my novel's subject matter?