I've had some for better than five years. No spine loss, that I can tell. I don't shoot every day. I do hunt with the same arrows every season, just check, striaghten, and re-seal if needed.
I'm using cane arrows now, and love them. Little harder to build, but seem to be tougher.
Port Offord cedar, Douglas Fir, Ash and Hickory are all in my extra quiver. Just get the best shafts you can find, and they'll all last for a long time. Don't skrimp on the quality. There are several sponsors on here that can provide you with good wood and info on how they stand up.
Hope this helps.
JAG/Johnny