Campangnolo recommends every 20000 km (12500 miles) on their cables for the kind of use you describe.

Zinn the author of "Zinn and the Art of Road Bike Maintenence" recommends recableing every year as a prevention for problems. That seems excessive to me, but there you have it.

Bottom line: keep an eye on your cables, don't ignore things like increased resistance, bb routing, a drop of oil on the brake cable/ housing interfaces, look for fraying, oxidation and so on..