should i have hardended exhaust seats installed

I have always heard non hardened seats don't last but I've got a buddy with a Challenger that he rebuilt a 69 440 magnum for in the early 80's. Since then he's put nearly 40,000 miles on those original non hardened seats without as much as adding a lead additive even once and it still runs fantastic. I'd say if they weren't freshly done have it done but since they are and you only put 500 miles a year on it run em like it is. Spring pressure also affects how quickly they'll wear out so that's something to keep in mind.