How much home AC voltage variance is too much?

I have been measuring my AC voltage of my dedicated circuits for my audio system. During the past 24 hours, the voltage has ranged from 121.5 to 122.3 volts. Is this too much variance? Is this too much voltage, given our target is 120? What is an acceptable voltage variation for most high end amps and pre-amps?

I am also wondering whether or not to pursue an AC voltage regulator or regenerator. Additionally, I am considering a balanced power conditioner, such as the BPT 3.5.

Any thoughts would be helpful. Thanks.