If you don't vote, you have no say. Others will determine the result. The few people who are ardent party supporters will determine the election. The one issue crowd will have more power than you did. Besides the presidential selection, the down party candidates are just as important. Neither Romney nor Obama can accomplish their agenda that they are promoting in commercails if Congress is controlled by the other party. Until I studied state law in law school, I have no idea how the most basic items are determined at the state level.
I also think that voting indicates a world view and life style choice. Voters tend to be doers in general. The mere act of voting represents a lot. You believe the process is important. Powerful lobbies have an extraordinary influence on public policy and the definitioin of issues. Clearly, this is a valid right. Unless individuals become involved, there is little curb on their influence. Even if my vote is only symbolic, it has meaning. When I talk to friends about their bureacratic or legal problelms, those unwilling to write to corporate offices or government agencies, are unlikely to get what they want. Passivity or the JW neutrality take makes us victims. My personal voice is just as important as the voice of anyone else.
Across the world, activists are tortured, imprisoned, or murdered fighting for the right to vote and fair elections. Voting is viewed as a birth right here. I agree that the candidates present no meaningful difference in the long run. People should be precluded from complaining unless they vote.
Don't participate in politics at all and you will certainly have no voice and end up with little.