I posted the US '05 Mazda3 changes in the thread titled ''05 US-spec Mazda3 changes'. US-dealers can no longer factory-order a '04 Mazda3 (the last '04 order allocation has passed). However, of course, they can still do dealer trades and other trades/pickups at the port.
Basically, the longer you wait for a car, the more updates will be had at the factory. But if one goes by that theory, then you'd have to wait until the final year of production to get all the upgrades that the factory has learned about a model. So it's a trade-off, waiting will have more updates but the model would have been out longer, and also prices generally rise slightly for each model year (heck, Mazda Canada raised the Canadian-spec Mazda3 MSRP by $100cdn during the '04 model year). So it's your choice, my philosophy is to simply get a car when you need it.
Any potential Mazdaspeed3 is way off (at least 2.5yrs from today for N. America, and that's if there is one at all).