"the failures of the Church do nothing to bring me closer to God, whereas my own failures can, and should, lead to growth."
I guess it depends on how one views those failures of the Church.
As to the last point, the fact that you included the word "should" is instructive in my opinion. A lot of things should happen. We should follow God without sets of rules. We should do a lot of things. Being human makes the world of "should" moot. And if you continue to repeat your own failures, what growth is there?
My sticking point with individualism and humanism, is that it is wholly incapable of divining the Truth. Good, smart and God fearing people read the Bible and come to different conclusions on an hourly basis. The Truth isn't relative to their specific contexts, it's an absolute Truth. The inability to answer these questions definitively is where the concept of Humanism always fails, and it's something I've never been able to get on board with.