I think one of the difficulties here is that you usually have to take the MCAT after only 3 years of classes, and usually the good, useful science classes are upper division classes with lower division prerequisites, so you only can take advantage of one of your two years worth of potential knowledge and experience when taking the MCAT. Then again, I think people make a bigger deal about the MCAT than it really is. True, it can help you if you are a little weak in other areas, but a great MCAT and gross weaknesses other areas isn't going to do much for you.