OK i just thought of this while i was reading through some history of tanks. My idea is for all tanks/vechiles of the ostheer to have a large range of verterancy options. For instance 10 levels of veterancy, this would simulate the relative inexperience of the new crews due to difficulties training them late war, and it would be a more gradual upgrade, also mean that there would be a much greater need to preserve units. What i would suggest veterans wise is accuracy, firing time, and maybe special abilities, like German might (or something), acts like heroic charge for tanks/infantry. Vetrancy IMO shouldn't effect how good the armour is, although possibly could effect received accuracy (veteran crews know how to dodge fire obviously).
(Conversely) Another idea is, that at various levels of veterancy the tank would change appearance and functionality to represent the changes to tanks over the war. For instance (and i know this isn't historically accurate but its the only example i can think of) if you have a panzer IV, it starts with the pea shooter and the armour that it was originally designed with, and as you progress through the veterancy levels, it gets better armour, up-gunned, side skirts etc. This would probably have to be used in conjunction with more common vetrancy upgrades, if the idea is used.
also, due to the high levels of vetrancy included, i think it would be a good idea to be able to have the crew bail-out of a tank when its destroyed or when the player decides to. When bailed out of, the crew would destroy the tank, to represent how The germans treated there broken tanks in WW2, don't want to leave it to this filthy soviets. to make sure it isn't completely op, it would need to be governed by couple of rules.
One crews couldn't retreat, they would have to make there own way back to base, this would emphasise the need to support your tanks, in case your vetran tank crew has to make a run back to base.
secondly the bail out ability should be an upgrade, or a situational thing, which costs resources. Either you buy a global upgrade, to allow crews to bailout of tanks, when you want them to, blowing up the tank, but allowing the crew to fight a nother day. or you buy the ability to bailout on a pertank basis, for a price i.e 5 fuel, 50 munitions, 100 MP to bailout whenever you want ( instaneous upgrade).
thirdlylosing anymembers after they have bailed out would effect there veterancy level i.e minus 1/5 of the veterans level (to indicate that losing one man in a 5 man crew would make them a 5th less effective)
Just thinking about this it would probably also be a good idea to allow a contingency method to make sure people don't accidentally blow up there tanks, i.e when bailed out of, theres a 10 second fuse on the tank, which can be cancelled out of.
On the plus side, when they get back to base, you can get them to man the next tank to come out of the production line (i would suggest any vechile, just because you may not have much need for a vet 8 tiger squad, when you only have the resources to build a puma).
well that's my idea for the vechiles, and even it isn't adapted, i hope you guys can still enjoy the idea