I got a 3.9 (out of 4) in first year engineering without going to a single lecture. Can I get a 4.0 easily if I go to all my lectures in 2nd year and beyond?
Either way you should go because you never know when the professor might drop a hint about the next exam...
Words of wisdom. For this reason I have still attended lectures of a professor even when I was gaining no insight in the classroom at all (he was that bad). Learning is all up to you, but if there's a minute chance that you may get a hint on what will be on an exam, don't miss that opportunity.
Just to offer a different perspective, I really enjoy lectures. I find that reading the material, working through it myself, and then having it explaining in a lecture format is very helpful to me. Also, one advantage of lectures I've found is that its much easier to find information on the topic. Professors may drop a key/buzz word or a very interesting problem/solution and from there the individual research can go much further. Also, I am a fan of longer lectures (~2 hours). The shorter ones sometimes feel like just an introduction, whereas a long lecture can feel much more in depth and analytical. Just a counter thought!