Not being able to plow through 18" of snow with your FWD Mazda 3 is much more an issue of clearance than traction. You can only push so much snow with any given amount of traction. The OP has better clearance with his Highlander, and will likely never see even 12" of snow outside his Fort Collins neighborhood in a big storm every year or so.
Did I mention the time Eric high-centered his BMW 3-series backing out of the garage in Longmont? He had to dig out the snow under the car to get back in.