The flaw with your thinking is you don't actually know what was important or worthwhile until after it happened, and it may take years for that to really play out. Some of the best employees and friends I've ever had came about through an unproductive hour or two, filled with argument. As much as we'd like to think we can judge interactions within a few minutes of them happening, we can't. The funny thing is, the same rule applies...to startups! When you try to compartmentalise and distill everything into a snap judgment you just end up making mistakes and missing opportunities.

You're not gonna bill me for reading your comments, are you?

Spending an hour of your time in a discussion which helps you reaffirm and/or challenge your own beliefs can be incredibly valuable.