Shock cooling at approach speeds is one of those furphies that some still believe in. So, the position of cowl flaps on final probably does not matter either way. Or for the short duration of a missed approach. Whatever the POH says is OK by me.
As for checklists on bugsmashers, these days schools and clubs need to cover the lowest common denominator, whereas in times gone by it was left to Charles Darwin to sort out those unfit for the task of flying. But the idea of writing a checklist with non pertinent stuff like gear and prop pitch when the aircraft is not fitted with these items seems counterproductive in that we will then have certain pilots who will regard the checklist as a bit of overkill.
I was looking at a very nice early Piper Cherokee recently. It is on the N register, so has FAA mandated placards in the cockpit. The placard for takeoff has 8 items and that for landing 4 only. Sensible stuff like fuel on most appropriate tank, mixture rich and boost pumps on. Incredibly, in over 40 years of flying under several owners, this aeroplane has never crashed.
Good enough in its day and still good enough.