Well, it appears I should have read Mankiw’s post much before:
Avoid activities that will distract you from research. Whatever you do, do not start a blog. That will only establish your lack of seriousness as a scholar.
Hmf. Next advice gives some comfort:
Remember that you got into academics in part for the intellectual freedom it allows. So pursue your passions. Do not be too strategic. Be wary of advice from old fogies like me.
Should I disregard the first advice? Or the second? Both, perhaps.