From the sounds of it, you are relatively unfamiliar with house wiring, circuit panels and the like. Most of us are so don't feel bad. This being the case, I for one would highly recommend that you hire an electrician if you are going to be running new wire. As far as changing the circuit breaker in the panel to a 20A, it likely isn't that simple. The wire running to the oulets has to be rated for that current as well. Odds are the wire that currently exists is only rated for the standard 15A.
Regarding some sort of power regeneration/filtration, it really depends on a lot of issues. Being that you live in a relatively new area, I would imagine the power isn't too bad. However, if you've ever noticed noise or 'pops' coming from the speakers when something like your refridgerator kicks in, then it might not be a bad idea.
At a bare minimum you should have some sort of surge protection. This will help (not guarantee) protect from lightning strikes as well as other large surges that may occur. Lightning is not the only cause of power line surges. There are also power lines being knocked down, clumsy power company workers and so on.
Finally, to determine how much power all your equipment is pulling, just add up all their power ratings and divide by 120, that will give you the MAXIMUM current it would pull. For instance, your 600W sub would pull 5 amps at max power. However, it is highly unlikely that the sub amplifier will every pull that much power. If it were, the sub would probably be distorting and clipping. It really doesn't take much power to make speakers get loud. You can run a surprising amount of equipment off of a single 15A circuit because of this. On the other hand, things like a vacuum cleaner really do pull close to what they specify, like 10-12A.
Of course, to be extremely conservative, just go by the max power ratings on everything, that way you have a lot of extra room for safety.
