As for dwindling book sales, yes, there are book trades going on, but they are usually for older books or at least books that have been around for a few weeks. And, in our "I want it now" generation, fans of an established author will not hesitate to buy a book from a bookstore when it is newly released. Same thing with new authors who win prestigious awards (I can only imagine how the book sales are soaring for Yann Martel!)
As for the rest of the new authors? Well, I think the rules remain the same for any author/musician/artist: establish a fan base. I'm sorry if I seem idealistic, but if you write a good story, then people will buy your book. It's as simple as that.
The desire to get rid of anything that re-distributes books (2nd hand shops, libraries, book exchanges) irks me somewhat. I'd like to think that books are much more than the "consumer good I paid X-dollars for". They're a source of entertainment, enlightenment and inspriation. We should definitely support our authors, but if it turns into an issue where books are only obtainable by those with money, then we run into many, many more problems that, in my opinion, are much worse than dwindling book sales.