If I remember correctly, it wasn't even built for this purpose. Wasn't it first built as an indoor football practice facility? And hasn't it literally been falling apart since the 1950s (when an exterior wall collapsed)? I mean, you can legitimately argue that it's been a temporary home for these sports since the building was repurposed for them how many years ago.
On the other hand, it's a very nice home as temporary homes go. Not great, but they've made it into a good competition space with all the improvements over the years. They could probably preserve that building indefinitely and continue to refine and renew it. It's certainly eligible for the National Register; is it on it?
One way or another, the current building within its constraints cannot be expanded or modified to provide the amenities that fans have at other venues. In order to realize that, you'd have to reroute streets and do things to the building that would render it unrecognizable, at least from the outside. If that kind of fan experience is considered essential, then it IS time to move on. If us fans can tolerate things the way they are, we have other societal needs.
I was recently told that program insiders consider the building a major recruiting disadvantage--that today's recruits look at that old building and roll their eyes. I'm not going to dismiss that assertion out of hand, but it's reasonble to be skeptical. We swallowed what the Twins said, hook, line and sinker: that if we built them a new stadium, that it would translate to better players and more wins. I believe they have a losing record since they moved into Target Field, and of course, they haven't won even one single playoff game since occupying the building.