Actually, I didn't realise you had four roles, and thus four (or more) machines. But, given that new piece of information, I would argue that keeping them all in sync is a good idea, too.

This doesn't mean you can't upgrade. It means that you plan and schedule your upgrades. You plan an upgrade to your dev box. If your white-box testing fails to find problems, you then proceed with build/test upgrades. Once everything is tested satisfactorily, you proceed with the production upgrade. Everyone (all affected parties - mostly managers) has buy-in at each stage. If intractable problems are found (hopefully prior to production), you roll back to the previous level. Perhaps you get to that point, and decide to try a different level. But your production server isn't affected until you have something that works.

And, yes, this makes the whole initial question pretty much moot. :-) That's kind of the point - to solve the problem in such a way that lots of problems are solved, rather than a band-aid for just part of the problem. Otherwise, you end up in a project of band-aids, rather than a robust, well-tuned machine. Remember - the point isn't to write code, but to produce revenue. And I presume that the production server is critical to that last part.