it should take resources to recrew them -both repairs and mp/fuel
Honestly, unless you make it cost 70-90% of the initial resource cost, being able to recrew enemy vehicles just swings the game too much for an RNG mechanic. Recrewing enemy vehicles on the spot and then have them perform regularly hardly makes sense logically/historically, it would take time to figure stuff out and get used to.
At worst, captured abandoned vehicles should also have significant combat penalties like -25% to -50% of everything (mobility, reload, accuracy, etc.). Again as a means to lessen the impact on a game.
But I'd rather just see recrewing removed in total. I think it would be better if abandoned vehicles simply couldn't be recrewed anymore but instead could be siphoned/salvaged by engineers for some extra resources (in CoH2 terms maybe 50 ammo and 30 fuel tops). Make the process take quite some time so the wreck has to be properly secured first. On the front lines this would still have the desired effect of creating a random and sudden extra objective to fight over and secure. If it happens behind your/enemy lines then you or the enemy are/is lucky, but a relatively small amount of resources isn't going to swing a game.