Mike,

Modern Electronics in vehicles are designed for "tow truck driver jumps"... where they zap you with 24V to get that starter spinning.   It has been a design requirement for some years now, along with load dumps, over voltage conditions, etc for the automotive applications.  For the EE's in the group, the old 7805's (14V max way back when, new versions are good for 35V max input)  gave way to the LM2931's series regulators which tolerated 26V inputs,  which were superseded by LM3480 that could withstand 30V on the input pins.   Catch is your old 12V Narco radio may die with 16V inputs (guess, haven't measured it*)

Alternators to still fail in overcharge conditions, but the subsystems can withstand the high voltages.  Yes, the battery gets boiled dry and will soon fail, which is often the first indication of the alternator failure.

If you keep alternators cool, which keeps the electronics cool, you can get a long and happy life from voltage regulators.  In years gone by with aftermarket 100W light for my Rally Car's I used to kill alternators on a regular basis. In sever cases the ol' Hitachi alternators got hot enough to melt the solder around the diode.  

These days a simple 'replace brushes' and inspect bearings at 100K miles is all that is required.   That and a simple "big RED LAMP" to get your attention that something isn't right.    Overvoltage crowbars are a good thing, but really depends on the electrical item (i.e. if the ECU can tolerate a 24V input, but the crowbar shuts off power above 16V.... oh chit man!)

*I have a HP 200W supply.   10Amps at 20V, etc.  I'll be glad to test you aircraft electronics at 20V to learn which things die as I ramp up the voltage. I've never gotten any takers on my offer, as it may kill your nav/com equipment.  I do like ramping it up to keep track of current, and when relays open and close.  Ed A -- HP6033A power supply.  Also nice to learn when all the relays go "thunk" as they open!  :)

Tom