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

NO!

Too much power generally isn’t an issue when pairing hi-fi /home theater speakers and amplifiers. It’s the opposite situation—too little power—that can create problems. When an amplifier is driven into clipping (distortion) by being asked to produce more power than it’s capable of delivering, the voice coil of the speaker it’s attached to can overheat and become damaged. That said, an RMS power rating on a speaker doesn’t even begin to tell the whole story. Two other specs, sensitivity and impedance, are much more important in determining how much power a particular speaker requires to deliver sufficient volume levels.

Ya, too much gain.

Rock "in" Roll

.

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.