Dedicated power....

Depending on the type of amplification you are using a 20 amp circuit may or may not make a difference. As far as using high quality outlets go they can help and certainly can not hurt. I believe a good quality hospital grade outlet is fine but others will differ with me.......so to each his own. I personnally use PS Audio Power Ports and I am very happy with their performance. And I figured I went through the trouble to run the circuits I might as well go a step further and buy the better outlets.

It won't make any difference unless you change the size of the Romex back to the breaker panel.

Typically per NEC:

12 gauge wiring for a 20 amp max breaker
14 gauge wiring for a 15 amp max breaker

And to add to what Forrestc writes:

If you're going more than 15 or 20 feet from your panel, go up another wire size to make up for voltage over the distance.

20A = 10ga.
15A = 12ga.

Are changing the outlets easy.

Sorry, the sentance should read "to make up for the voltage LOSS over the distance"
.