"What about high powered, high performance machines, like the humble Aerostar, which is completely devoid of cowl flaps?! They seem to get by in hot parts of Australia just fine without them!"
If they do then they are simply unnecessarily overcooled in the cruise and suffering from excessive cooling drag.
Talk to any high performance non cowl flapped kit plane owner about spending undue time on the ground with the engine running.
If you want to see what a 540 donk install looks like on an aircraft that spends its time at high power and low speed and lots of ground idling then look at the size of the cooling outlet on a Pawnee. And still you can get them so hot you can actually feel the powering dying.