I guess if true 5-passenger comfort is needed then yeah, you'll have to shop in the mid-to-full size segment. If it's only every once in a while any of today's overly tall compact cars are plenty comfy for 4 people. The upright seating position takes care of that.

Regardless, for mileage I'd stick with a 4-cylinder rather than V6, so that rules out the Maxima, and means I would have spent my time at the Chevy dealer looking at a Malibu rather than Impala. Newer platform, and actually has a 4-cylinder option unlike the Impala.

You also may as well also go check out a Hyundai Sonata while you're at it.