It still works, this "higher elevation = cooler temperatures" thing. Right now most of the U.S. is burning up while here in the Rockies we're comfortable without air con.
You wouldn't want to spend winters here. The winters are both cold and long; that's how a hill station works. We spend the cool summers here and leave the long, frigid winters to the year-round residents.
----------o--0--o----------
The great central valley of California, from Redding in the north to Bakersfield in the south, gets beastly hot in summer. Temperatures over 100 degrees Fahrenheit are common. Places in the Sierras like Burney, Shaver Lake, Lake Almanor, Quincy, and Lake Tahoe were the valley's hill stations.
Before air conditioning lots of valley families had a summer cabin up in the Sierras' piney woods, a fair number still do. Mom and the kids would spend the summers there and Dad would drive up on weekends.
Of course, air conditioning has made hill stations less of a necessity and more of a luxury.