Really? Hm, I'd think it would still be a good idea to do a reading even if the book won't come out until a year from then. Hearing the right part of a story can plant a seed that will slowly germinate until they see your book and go "oh yeah, that was a cool reading, I should get this!"
I admit that the readings I've enjoyed in the past are mostly of authors whose books I've read before. Lois McMaster Bujold used to always do readings at Marcon before she moved to Minnesota, and she'd always do the book she was currently writing.
I'd include readings as a part of marketing. Sure it's nice if they can buy the book right then, but if you don't have a book to sell right then I still don't see that it would do any harm to do a reading. Except that it might be tiring, or maybe you're bad at reading out loud, or maybe they schedule it during a panel you wanted to go to.
But I've also heard that sometimes editors drop in at these readings. I heard mention of someone with no contract anywhere who did a reading and an editor was there and bought the book. Of course that's likely rare but still, if you get in the program and they can look your name up and see that you have a book coming out next year, they might say "hmm, TOR thinks he's good enough, let's see why."
Well. Anyway. Maybe you already thought about all this, but I thought I'd bring it up.
On an unrelated note I see that Worldcon 2006 will be in Los Angeles. It seems likely that I'll still be in CA in a couple years, so I'd definitely go to that one if I end up not being able to make it to this one.