I like the Impala for what it is. A nice big FWD sedan ready to swallow cargo and leave occupants with a good amount of stretching room. The LS that he reviewed is pretty basic as I've also sat in it. If you need a no frills, point A to point B basic transportation, the Impala LS is it. Although you could compare it to a 300C, FWD does take precedence in some states.
For me the Impala would be one of my top choices for a big FWD and inexpensive car. The four-speed auto is fine with me, the Impala achieves good gas mileage with the 3.5l V6/4spd tranny combo and granted a 5 or 6 speed would most likely pump out better MPG, but the powertrain is reliable and I value reliability over bragging rights. GM is slowly incorporating 6spd transmissions on their newer cars like the Saturn Aura which I'm sure you are aware of. I'm just waiting for the reliability records to be proven before I make a jump into newly designed transmissions.
I've had enough fun bringing my 02 Accord in for 3 new trannys. None of them had ever broken or left me stranded but they all made weird whining noises or would shift into gear harshly and the dealership agreed that my car would need new ones. I still love the car though as I think its a sleek coupe for the money but now you can see why I prefer time tested powertrains over new ones.
In the end however, regular customers will look at the sticker on a car, see how many cyl the engine has, glance at the MPG numbers, and not give a second look at whether the transmission is a 4, 5, or 6 speed, as long as its good they'll buy it.