Henry, the age-old question! IMHO, you need to ask how good a sail do I need? The answer is as good as your crew, boat, and competition. Sails start degrading the moment you raise them. I club race and average about 70-100 hours a year on a main, roughly 40% under 10kts TWS, 50% 10-20 knts, and 10% above 20. I'm fussy how we flake it and don't flog it. I use a Dacron x-cut main for 3 years - I notice upwind performance (pointing, etc) diminishing around the end of the second year, hurting in the light conditions first due to loss of smoothness in the panels and loss of overall shape. Physical signs of age are loss of fabric stiffness which results in unwanted wrinkles when you ease halyard tension, max draft moving back towards the leech, growing backwind "pillow" from the overlap, leech telltales that don't fly well, a sail you can't flatten as much as you would like. You can milk more life by replacing battens (they age too), using a low-stretch halyard, generally honking on the corners more, and trimming appropriately for a fuller sail (more twist, higher boom, etc.). Sailing World had an article on sail shape a few months back that might be worth checking-out. Fresher sails are always better. Just takes the budget and the rest of the program to benefit from them.
