But thought can be worse than action - thinking quickly spirals into brooding. Pardon me for yet another misrepresentation of depression, but I confuse it with boredom, albeit in an existential sense.
Zazen encourages us to meditate on our breath and to observe our thoughts so that they hopefully melt away. It asks us to think less, not more; to shut down our internal monologue which is the biggest agent of human misery. The trope of the mad genius is true - there are three great books that touches on this subject: Hesse's Steppenwolf, Colin Wilson's The Outsider, and the amazing Logicomix. Also a recent research surfaced on HN on neuroticism and the dangers of self-generated thoughts - http://www.sciencedirect.com/science/article/pii/S1364661315....
There is however a kind of thought that _is_ action. The state of flow when deep in deliberate thought, trying to solve hard problems (hard is relative to the person thinking it) is amazing. That kind of thought is very different from thoughts about the self, or doing drugs looking for profound realizations - there unfortunately isn't anything deeper about life that we'll be able to figure out by random introspection. Science is our best bet for that; not LSD, not meditation, not boredom.