I think there's a false dichotomy here. Memorising a dictionary is easy, because memorisation is a choice (with spaced repetition). Reading a book in an unfamiliar language takes lots of time and mental effort. Both will contribute to your understanding of the language; perhaps memorising a dictionary contributes less, but then there's a lower activation energy involved in it too: whenever you have five minutes spare, you can just sit down and learn a couple of cards.
Thanks! I guess I never really thought of going over cards in spare time. In retrospect, that might be why I never got into them. I only used them when I had a lot of time to dedicated towards learning the material anyway and then I preferred reading.
