FWIW in my '06 spec 4dr I used Kenwood 1665's in front and back. It's pretty good for listening to rock, but the mids/highs are definitely stronger than the bass. Of course I don't have an amp or a subwoofer, and I used some of the cheapest speakers that were available. However, the improvement over stock was substantial, and listening to dubstep, electronic music, and light alternative (mumford & sons, jack johnson) is phenomenal!
I should have been more clear. If you look at Crutchfield, they tell you exactly how it fits on the item description page. For example, the Kenwood 1665 has an advisory under the price/add to cart area with a yellow triangle / "!" It says "Fits with bracket." Bellow that is a link with installation details. This explains that the speaker will require a bracket for installation, which is included for free with the purchase. The wiring adapter to go from your aftermarket speakers to your stock wiring harness is also included for free.
Don't worry, and go with crutchfield. They will take care of you. :thumbsup:
The door and rear panel speakers on Spectra's 2004.5 to 2009 are 6.5 all around.
Spacers or adapters are needed for the front speakers and maybe on the rear.
Crutchfield will include the front spacer/adapter. For the rear, I removed the guts from the stock speaker and bolted the new aftermarket speaker to the stock housing. Fit like a glove and sound great!
When you install the front door speakers, please make sure that you lower the windows to make sure the magnets aren't coming in contact with the window. It would suck for you if you take apart the door panel, install the speaker, but then you can't lower your window all the way down.