Note that it's only 55psi on the front end. Rear end is lower. I get a really nice ride out of mine at the recommended pressure, and good mileage. You can get a slightly softer ride on a softer tire, but your mileage suffers because of increased friction due to sidewall flex. Also, the tire sidewalls start to heat up, especially on long trips and higher (highway) speeds. The lower the pressure, the greater the effect. This heating degrades the sidewalls.
I've seen the results of a tire run at low pressure on the highway on a hot day. The sidewall actually smoked and blew out. Kid said he knew it was low, running 20 lbs instead of 35 recommended for his car. He didn't think it would hurt anything. He drove 2 hours on the highway at 70mph. Then the tire blew out and he sat on the side of the road until a tow truck came. (no spare) Meanwhile, the tire kept smoking for about 10 minutes and we got his wife and kids out of the car just in case. The sidewall of the tire, aside from being super hot to the touch, was crumbling apart on the inside and outside, as it sat there.