Can a power amp have too much power, risking damage to a speaker?

Ya, too much gain.

Rock "in" Roll

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You'll likely damage your hearing before the speakers 

Technically yes, you could damage your speakers with over wattage, but as someone stated, your ears would probably be damaged first. There is more risk with an underpowered amp that starts clipping at high volumes, this will trash your speakers much faster. 

THANK ALL of you for usefully responding to my query.
My overall take-home: an underpowered amp driven to clipping seems more likely to damage a speaker than clean power that controls the linear motor of audio transducers. An amp driven at its upper limit is more likely to clip tops of waves, causing the voice coils to stay in one position just drawing current [may not have said it perfectly]. 
I still have great hearing even after being in a rock band during my 20s [took great care to protect ears during all performances], and we often get out an audiometer to ensure the sound-pressure-level is well under 95dBA for sustained periods. So far, so good! 

There is no such thing as too much power. It is far more common for an underpowered amp to destroy speakers with clipping which can easily overheat fragile voice coils.

High powered systems are always limited unless you like destroying your ears. K horns will easily destroy your ears before they get into trouble.