Yes! Decline meetings that you have nothing to contribute to and nothing to learn from! Don't be bashful about it. Maybe I'm extremely lucky, but I've never worked at a place where there was this weird taboo against declining meetings. We're all grown-ups and presumably were hired partially because we know how to manage our time, so manage yours!

I'm double- or triple-booked for most hours of the day. I casually decline meetings all the time and don't sweat it even in the slightest. I don't recall the last time someone asked me, "Hey, you were supposed to show your face at Meeting X, why weren't you there???" This happens in crappy companies.