It doesn't strike me as particularly effective either--more symbolic than anything else. I can appreciate the gesture, though. And isn't that what this largely is? Part of the idea is that hopefully, somewhere out there is life. This is sort of a way to reach out to them. It's very human to me--reaching out towards the unknown, hoping for someone to be there.
I'd like to think there are two ways to think about life--either everything's futile or some things are meaningful. I don't think there's a decisive way to prove one or the other wrong.
On the scale of planets and galaxies, I existed for a short time--hardly any time at all. But I experienced it. These things did not. And even though I'll fade, and they'll stay for another couple billions years, I'd rather have known than not known at all. But each to his own.