Ward Cunningham's 'Technical Debt' discussion is a favorite metaphor to help the business relate why not all IT spending can be on new features. However, after a crazy semi-annual install, I find that perhaps there needs to be an extension to the metaphor, the Gremlin Bond.
Homeowners in the South are familiar with a form of insurance known as a Termite Bond. We pay an exterminator to regularly apply pesticides and bait traps around our homes to ward off infestation. To wait until you see evidence of termite damage is insanity. At the point you know the termites are there, you might as well start shopping for a new house.
Code gremlins also quietly accumulate, often asymptomatically, until it's too late to remedy things without going to scorched earth and rebuilding from scratch. Time spent writing automated tests, refactoring, code reviews, and upgrading system components is the Gremlin Bond. Less sexy than building a new house every couple of years, but far more predictable and therefore manageable cost over time.