I think you dramatically underestimate the benefit of writing a formal model! I've run classes where we've managed to discover bugs in the client's actual production system with an afternoon of modeling.
How important is it to discover new bugs? Surely any large production system already has a backlog of tons of known ones. So if I want to fix bugs in my system, I can just go to the issue tracker and pick one.
Depends on what "discover" means. In the sense that Hillel is speaking of here, it probably means more like: Discover the bug exists and also discover, to a very high degree of certainty if not absolute certainty, the location of the bug in the code base.
That discovery is actionable, many other bug discoveries are not without further investigation.