Data point: I have definitely been engaged in "sub-optimal levels of careful introspection" for most of my life. Articles on Less Wrong prompted me to introspect more, and the benefits I've gained from doing so have definitely been greater than the expected benefit from anyb obvious alternative use of that time would have been.

I'm not sure whether the current amount of resources I spend introspecting (after LW's effect) is greater or less than optimal, but overshooting a little is probably better than undershooting and missing insights.