For me once a new Titleist driver comes out, I get it!
A three wood can stay in the bag for years, same with a hybrid. Find something you can hit straight and always have it in there!
Irons can stay in my bag for years, often 4-6! I am still playing the 710 CM MB, they do however need a checkup at the loft and lie doctor.
Wedges need replaced every year.
As for the short stick, there might as well be a revolving door on my bag, shot even par with 3 different Scotty's this year. However my latest setup, a Golo S with a SuperStroke may have some staying power.