A single quality subwoofer is often enough for a single room, for most people, in terms of SPL and even bass extension. But a second subwoofer can provide smoother bass throughout the room, and solve subwoofer placements issues. Whether that respresents value to someone or not, there's still solid science behind it.

80 Hz is simply a well thought out crossover point for the vast majority of systems sold. But that doesn't mean it's the best crossover point for a capable system, with good amplification, in a large room.