It is worth voting to me only if three conditions are present: (1) I have some kind of interest in the election, (2) There is a candidate whom I want to win, and (3) I can trust that the outcome of the election will be a result of the votes that were cast.
With that said, I don't vote. I don't actually believe in representative government, especially the way it works in the United States, but I would participate if the system seemed legitimate and there was a worthy candidate. Unfortunately, politicians are largely scum, the government is corrupted from top to bottom, and much of the electoral system is run by a politically-aligned private corporation. Voting is basically renewing the lien on your tax money and re-surrendering your political power to corporate America every couple years.