Our wet cell batteries are all factory originals, putting them close to 7 and 3/4 years. Like Jim I check water every few months, more often during heavy summer use or long term plugged in situations. Unlike him, I don't have the auto-fill system for the house sets, but having grown up on a farm I don't deem it a hassle to maintain them. Dad's '62 pickup and '52 tractor bats commonly went 12 years.
I just changed out the factory bat in my '97 F-150 a couple years ago. Granted, it was a no-maintenance one; but the point is if you don't let a battery or set go completely dead anytime during its life, chassis or deep cycle, wet cell or otherwise, and keep it clean and charged, it should last barring any physical damage. The worst thing on a battery is when some electrical device drags it way down while the owner is unaware; chassis batteries especially are never the same again.
Given all that, just like Jim I am not one to spend the extra money on glass mats. But if you're not into water level maintenance at all, they may be worth the expense.
Joel