The exterior of a coolant hose seems to last forever nowadays, but it is the interior of the hose that degrades by simple friction alone. And that is exacerbated by hot climates, not exclusive to them.
Doesn't take a lot of degradation to see buildup in cooling systems. A build-up of less than 1/16 of an inch can cut heat transfer by 40%.
In other words, why cheap out on such an obviously easy item to service, especially as it affords one the opportunity to examine other parts of the system for scale build-up.
In our JEEP (with incredibly high underhood temperatures due to poor airflow management), and living in Texas, two summer seasons is enough in my book. Coolant change annually, and complete cleaning and flush followed by new hoses/fasteners every other is simple, easy, and makes for peace-of-mind. Distilled water, G-05 coolant and some SCHAEFFERS #258 is working very well thus far. (But doesn't obviate the need for a chemical cleaning at Year Two).
Unless, of course, one is going to get rid of a vehicle before its true lifespan is reached. (Sort of, why bother with oil questions if other systems are neglected.)
If an interior inspection reveals losses of hose material too small to measure, then by all means keep them four years. Or ten.
I regard it as simple preventive maintenance (like replacing all fuses/fusible links/lamps every 50k or so; they do wear down.
I prefer the vehicle be as close to factory-new as possible so long as it is in daily service.
This approach has worked in my family for over a half century (back when it was 2-months or 2000 on oil, a tune in the winter, a major tune in the summer, coolant changes every 6-mos, etc).
