I agree with bmontani's comment on regeneration. Someone whose opinion I have great respect for suggested this. I bought a used Furman. At first, I did not have any sonic improvement, though having an UPS is safer for the equipment.
Eventually, I took my volt meter to the unit, and found out that the batteries were worn out. Replaced the batteries, and got one of the most significant improvements in sound quality. My wife (perfect pitch, incredible ears, doesn't care about equipment at all so no equipment bias) commented that it was much better after readjusting equipment parameters.
Other than the osiliscope, I don't think you can get a complete picture from any of the other devices above. Now, I'm going to suggest something I almost never suggest. I wouldn't bother trying to measure your outlet. From experience with sensitive scientific equipment, no unregenerated electric source is going to be anywhere close to ideal, so just using a regenerator is kind of a given.
Filtering won't work on its own since there is always line loss, and you are going to always have periods of low voltage. Having a power company hold at a consistent 60 Hz is also asking too much of distributed electricity. Some places will be better, some worse, but I can't imagine getting close to ideal anywhere.