Regarding the efficiency/maintenance discussion: (sorry if this comes off as "so last week")
What if "wear and tear" was no longer a function of a resource (machinery) but instead a timer like habitation for kerbonauts? Maintenance would be a function of resetting/moving back that timer through the workshop just like the colonization module does for hab timer. Resources required could match present requiremts for producing machinery. When a converter goes beyont its timer, efficiency rapidly decreases until the part "breaks", then a timer reset ("overhaul") would have to be done, just like in the Med Bay...
This could work locally or planetwide, or either by choice, just like PL vs LL.
The risk I see with total loss through failure is the mechanism of forewarning. As I understand it, all functions of base parts are only fully computed once in local range - so to get a reliable warning of coming (or even existing) failures, one would have to visit each and every structure regularly