Practical question on valuation of old systems

This reminds me of a (fictional) story...

A small New England town resolved to remedy a social problem. There was a (what's PC for "Village Idiot"?) person who was always at loose ends getting into trouble and generally being a nuisance. So someone hit on the idea of employing him. So our hero, call him Joe, was offered the task of polishing the Civil War cannon in the courthouse square every day in exchange for the princely sum of fifty cents. Joe discharged his duty admirably for a dozen years. Rain or shine, snow or drought, you'd see him carefully polishing the old artillery piece every single day. One day, however, Joe failed to show; then, no Joe the next day. The good townspeople, fearing that Joe had fallen ill or worse, sent a group of citizens to look for him. They found Joe in his little shack, well and in good spirits. When asked why he'd stopped showing up to his job, Joe responded, "Oh, I don't need to any more--I've saved up my money and bought my own cannon..." Cheers, Chuck