wattage

Loudspeaker specs can be a little misleading. According to your logic you might need 80 watts if the loudspeaker is a 4 ohm model. But that only pertains to sound output at 1kHz. It could take even more watts to produce equivalent levels from the lower midrange down into the deep bass.

As a practical matter 50 to 80 watts should be sufficient for 80% of the loudspeakers on the market in typical rooms. It's just that even greater wattage may be required if you want to optimized that loudspeakers performance.

This 1000x wattage issue is misleading. The math works and so does the logic, but it's not how your ears and brain hear it. Clipping and the dynamic compression that it produces can be very hearable and annoying, or it can be hearable and somewhat pleasant sounding, or it can completely unhearable. It depends on a number of factors.

Even with the newer class D amps, high quality-high wattage amplifiers are still expensive. In allocating money in a system I'm not sure it's wise to spend based upon what happens 1% of the time. I'm repeating myself, but a well designed 50-100 watt amplifier should suffice for the vast majority of circumstances.