GE rep stated in a briefing session earlier this week that excessive use of igniters through selecting cont ign on routinely had halved the life of the igniters for one engine type.
He also made the point that it's not just a commercial issue. Igniter deterioration also affected the functionality of the igniters, so they may not perform optimally when you really need them (say for a relight attempt in marginal conditions) if you've "used them up" needlessly.