No, the Mazda6 and Mazda3 don't have AWD.
Good choice on the Mazda6. If I was going to change my car, I'd seriously consider the new Mazda3 hatch, especially if they decide to make the manual tranny available with the 2.5L engine (currently you can only get the stick with the 2.0L engine).
Actually, even better would be if they drop the new Skyactive diesel engine into the Mazda3, again with the manual tranny.
As for trade-in value, you will almost always get raped by trading in your car. I replaced my 2010 VW Golf TDI (27 months old with 30k miles) with the Impreza because of the TDI's reliability issues. I was considering either the Impreza or a Focus, and both the Subaru and Ford dealerships offered me $16k for the TDI. I sold the TDI out of my driveway for $22k. So if you want the most for the Impreza, sell it yourself.