In all honesty, I don't think one can come down on one side of the issue. I really think it depends on how a person functions. I was a class-skipper. Many of my friends were as well. We are scattered across the spectrum in terms of class rank and boards scores. The same holds true for the class-goers.
I chose to skip class because of the way I learn and the lifestyle I enjoy as a students. I'm a late night worker, not an early riser. It makes no difference whether someones teaching the material or I'm reading it out of a book/syllabus. So I'd go to class, and daydream for five minutes, and then be lost for the rest of the lecture, and in that sense, it was a waste of time for me. But others learn better from hearing, and when they hear a professor say something, it sticks immediately, whereas they might have to read the same material several times to get it.
I really don't think sheer volume in and of itself is a factor. The volume is huge, but your efficiency in absorbing material during your time in class dictates whether or not you'd be more time-efficient in going or not going.
And I really hated the argument from the straight-arrows that I was "wasting my education and money." We learn however we each best learn. We pay money for facilities, availability of lectures, and most importantly, an evaluation and conferrance of a degree. If the lectures don't help you, why go? Guilt? Believe me, there are plenty of people who went for that very reason (at least amongst people I knew)
(incidentally, take my words with a grain of salt. Afterall, I'm an average student. Then again, I have a couple of friends who also skipped out every day, got hammered every weekend, and barely studied due to their incredible recall. They destroyed their boards and have plenty of interviews in very competitive fields. They're certainly not the norm, but I'm sure that both they and I have counterparts in the class-goers group.)