You should check out E-Bags (and if are a member of ClickRewards you can earn miles.)

Let me check out my bags:

Samsonite Garment bag: 8 years old, no problems (except my aching bag.)
Eddie Bauer Big Gym like bag: 5 years old, one zipper that I don't really need broke, but otherwise fine.
Eddie Bauer carryon: 6 years until one day dear Eddie decides to make it his bed and promptly rips it up and gets sick on it. Not a pretty scene.
Samsonite rollaway bag: about 3 months old. It's holding up well, even to Eddie trying to sharpen his claws on it. It does fit in the template because I hate checking bags.

So the average lifespan of a bag 6-10 years.

Good luck Dgolds and let us know what you end up getting.