First I side far more with the second than the first, but I would say it's not enough to go for things that are interesting. It's important to work on things that are inspiring. In my experience and in the experience of many I have worked with inspiration can overcome all sorts of obstacles.

But on planning, I am a huge fan of planning. I think one should plan extensively and in detail but then shelve the plan and not even look at it during execution. The real danger with plans is that they are inflexible and cannot take into account unforeseen developments. However, the time spent thinking through the plan places one in a position to do so. As Eisenhower said, "Plans are nothing. Planning is everything."