Hmm... Whether it's worth it to skip really depends on the course you're skipping. I'm mostly in arts courses (Classical Civilizations, English Literature, English Fiction with an actually good English teacher, Vocal/Choir), so if I skip, I really miss out on fun stuff. But I've got friends in the maths and sciences streams, and since they're pretty smart, if they only go to class to write the tests, they do fine.
At the same time, just because you get a mark for being able to do something, doesn't mean you value education. That you care enough to go to school everyday will someday serve you well, especially when it's up to you to attend class.