Local politics tend not to have a direct impact on national security or international affairs, but they have a huge indirect affect. First and foremost, any kind of nationwide movement needs to have local bases. Without them, they just can't gain traction. When someone runs for president, their army comes from local party offices that have been active the whole time. But the left is sorely lacking in these institutions.
On a broader note as to whether or not voting is a charade, no, it's not, but it's the most basic thing you can do. You need to drink water to live, but if you binge on junk food and get zero exercise, you can't turn around and say, "man, drinking water is such a scam." Voting is something that needs to be done to keep us healthy politically, but if it's the only thing that's done, we're going to be bloated and sick.
You don't want to vote for Obama? I don't blame you. I never voted for the guy, and never will. There's a slew of candidates you can choose from. And if you don't like any, write yourself in. Why? If people stop voting the message that will be sent will be "we don't care, do what you like." If there's a large portion of people that show they care enough to vote but hate the people in office, the politicians will have incentives to placate these people for their own gain. And that's what moves politicians.
People need to do more. They need to not only vote, but go out, organize, get into their community, start working on long term goals. And that takes time. And it takes numbers. You might be doing it, but we need to get enough people doing it (maybe 1% of the population) in order to get the kind of society we want.
And you can get results. The healthcare bill might be a bit of a mess, but Vermonts on the path to single payer: http://www.commondreams.org/view/2012/03/08-11
Like with gay marriage, medical marijuana, and soon decriminalizing marijuana, once commons sense solutions like these catch on, they have a tendency to hold. All of this is going on at the local level, and all of these could make big differences. But they're going to need people to support them (which will also help to build strong leftwing networks).
So I agree with you. Fighting for establishment Dems is a waste of time. And I do think that protests against the NDAA have more potential than other protest movements. But, I think there's a ton of good work we could be doing at the ground level that will have national impact, and we seriously need good people lending a hand.