This morning as I was driving to work I contemplated the aggressive tailgater behind me. My car's rear bumper has some paint dings from anonymous parking-lot damage that I never repaired (I deemed it not worth the cost for a cosmetic, not functional, problem).
I'm pretty sure that if the guy behind me had smashed my car his insurance company would have paid the full cost of the repair, restoring it to new condition.1 But what does halacha say, given that it wasn't in new condition in the first place? I have the impression (from vaguely-remembered articles and/or lectures, nothing particularly deep) that he is only responsible for the differential cost, but what happens when the only possible repair from the new damage (e.g. replacing the part) effects a complete repair? Would I owe him something to account for the prior damage, even though I wasn't previously willing to spend that money to get that repair? (That is, if the repair somehow restored the car to its prior state instead of a better one, that would have been ok with me.)
Does it matter if the pre-existing damage was minor or major? (Are paint scuffs the same as a pre-existing dent?) Does it matter if ignoring certain types of damage is common (everyone I know ignores parking-lot scuffs) versus unusual (almost nobody I know ignores major dents)?
1 Less my deductible, maybe. I don't know if that's relevant.