If braking heatload has never been to squishy/fading brakes and to boiled fluid, imho it may last long enough, at least i'd change never boiled fluid at most once per year. But then again if track is mentioned .. it's easy to abuse brakes above their capacity
. BTW, if you boil them often enough, maybe worth considering instead of frequent flushes change fluid to one with higher boiling temps / enhance cooling (eg. airducts) / reduce braking heat load (eg. shorter sessions / pedal dance instead of with nannies / braking lessons by hpde instructors ) .. or move to BBK.