Overpowering my speakers

Not really unless you accidentally turn the volume way up. 

No. Distortion from amps being over driven is what damages most speakers, not good controlled power. (Your ears on the other hand....go easy!)

Not really unless you accidentally turn the volume way up. 

This. Take some time learning what slice of your volume control position corresponds to good listening levels. It can be very nice to have more power than you need - no worries of amp clipping, which at least somewhat reduces risk to your tweeters. 

What can be annoying about having a LOT more power than you need, is that usually setups that have a LOT of power on tap also have a LOT of active gain in order to tap that power, especially gain after the volume control. This means that those gain stages must have an extremely high signal-to-noise ratio, or you will hear their noise floor in your highly sensitive speakers (even with volume all the way down) as a "shhhhhhhh" white noise sound. 

+1 @mulveling   If you find you have no problem with noise, L-R balance due to over use of attenuation then the additional power need not be a problem.