If you don't vote you have done nothing to even try to elect someone who you, in good faith, believe will do what you deem the right thing. Yeah, politicians are fucjing scum a lot of the time and lie to the point where its easier to trust the devil himself rather than a politican. That said, totally dismissing the system as one big huge scam is the lazy, cheap, and easy way out of your duty as a citizen. It's a total copout that lets you feel superior but in reality makes you completely inneffectual. The electorate may or may not have much power but it still has some. Voting is just one method of exercising your will over your government. It's important but we also need to be active in lobbying our government in other ways too.
Those in power want you not to vote. To take on this "I don't vote because its a sham" mentality is to play right into their little game. When enough people fall for it that's when it becomes a reality. I'd say its close to being a reality but it isn't too late to turn the tide. It's going to take some time which requires patience, something Americans don't have much of.
If you vote you always have the right to complain. If your guy loses you get to complain about how the other guy would've done things differently. If your guys wins and doesn't fulfill all his promises you still get to complain about how you were sold a bill of goods. If you don't vote, you're still entitled to complain but I personally won't take you as seriously because you haven't tried to affect change. This is supposed to be government for by and of the people but if you believe that Carlin joke (its a JOKE by the way) then it will no longer be that.