With regards to your question about the MCAT, the answer depends largely on what score you are aiming for. It is just about what you want vs. what you are willing to get it.
Now, in my humble opinion, though I believe that the MCAT tests your reasoning and critical thinking for the most part, the two come much easier if you have a thorough content knowledge. Personally, being a reapplicant and needing a stellar score (was hoping for a 520+), I memorized everything about the Krebs Cycle - order, enzymes, names and structures of the products, what compound inhibits/stimulates what, and I took this approach to as many concepts as I could. It's a reasoning test, but you can't reason your way without sufficient content. I received a 525 with this approach.
So you have to come to a decision on what your goal is, and what you can do to achieve it! But I do what to emphasize that the more knowledge you have, usually the easier it is to come to the right answers.