Yes I think you should vote, because if you don't vote it looks like you don't matter. And it is really hard to keep saying your unhappy about something when people can say that you voted and thus can't be unhappy.
Furthermore I'm really sure if the US Presidential election is democratic enough. Because of two reasons:
1. In fact you vote for members of the Electoral College and give them a recommendation on how to vote. Even though it's illegal in some states, they can vote different than the recommendation, this of course isn't really democratic.
2. The most states (one not I heard?) have a winner-takes-all system. The result of this is the possibility that although the majority of the people voted for person A, person B (1)