Do you have more examples of brute force approaches that have worked? I think it's often overlooked, and necessary even if you have narrowed the target audience as you have suggested.
I actually think that the problem I see more often is the opposite these days. Lean Startup principles have led more founders to build single features that a small subset of adopters might want, but little or no appreciation of why that wedge in the market will matter in a meaningful way.
Great advice - early as early as you can stomach or after the train has left the station. Most folks gravitate towards the middle ground where the risk/reward isn't really there.