Listen, Bobby. Your original question isn't really answerable as written, and you probably don't understand why. We can only guess at the intent of your question, whether to maintain a stable of workable but older bikes, or to focus on one (presumably better) upgraded bike.

So, to answer, one must take a philosophical stand of some kind. Along the lines of "function first..." or "I want to fit in on group rides..." or "I like to take advantage of trickle down advancements" or "I collect models of my favorite brand..." or "I like to tinker and maintain my older fleet..." or whatever.

What do you really want to know?

For me, I wouldn't have five similarly functional bikes of any vintage. Each bike must be able to do its job better than its neighbor, or it's gone. The only exception in my mind is where a good commuter bike overlaps with a very good touring bike. One bike could theoretically replace the other, or I could keep both. So, there's a philosophy for you.