I suppose this is a sensible approach, which equates to what we all probably should be doing with out cars, but I'm the kinda guys who keeps my cars until they die.
I'm 37, and my current car is my 2nd!!!
What I do is buy frames that I see for great prices, and I keep the ones I like and get rid of the ones I don't like.
With the ones I keep, I often ride them for a couple of years (with 3 "good" bikes going at any one time), then strip them down and build up one of the others. This adds enough variety.
Why get rid of a bike if you really like it?
However, I know a guy who continually trades up. He has one really good bike at any one time, and I think he trades up about every 2 years. He says he does just for a change, rather than any financial reason