is there a word which describes someone who confidently believes it's better to not dwell on some things?

I don't think I have the perfect answer for this, but let me try.

A practicalist - an advocate or adherent of what is practical.

I also thought about the words realist and conformist but I think they get as close to what you described as the word practicalist does.

This is if course ignoring the perfectly correct answer you mentioned agnostic because not many use it that way and a lot confuse it:

"agnostic, agnosticism". OED Online, 3rd ed. Oxford University Press. September 2012. agnostic. : A. n[oun]. :# A person who believes that nothing is known or can be known of immaterial things, especially of the existence or nature of God.