I think the process of making good decisions about "big" things should involve practicing making many more decisions about smaller things and evaluating the outcome.

There are a lot of insightful heuristics from decision making that can make big decisions much better/easier/etc.

I don't think people would spend any more time on big decisions if they made faster/fewer decisions with little "value" to gain, if anything I think their habit of making fast decisions would mean they spend less time/worse on the big ones!