Get mine done every 5 years, like the book says, about 36k on both the GT and the 156. The Tipex had only just faded from 5 years previously when I had them done again this year. I never buy additional cover insurance for white goods, the risks outweighed by the savings. if the belts go on the cars then so be it, I'll take it on the chin and scrap the cars. I'll let you know in 5 years time when they're due for the next change.
By the way, as a marker, about 10 years ago the belt snapped on my previous V6 156 at 55k, 5 years old. That was a company car with a poor service record and often driven by heavy footed youngsters in the office.