As a maintenance and reliability specialist, I always try to optimize equipment "uptime" at the lowest cost. Radiator caps used to be checked, but since labor is getting more and more expensive, they are normally replaced.
When my vehicles go in for service which includes the cooling system I request the caps be replaced. If the cooling system is acting up for some reason before its servicing date, the cap should be checked as a normal diagnostic procedure.
Similarly, when you buy new tires, buy new valves and valve caps at the same time.
The lowest long term ownership cost should always be your goal.