Amen, Wilbus!
I posted similiar propostion in the Gameplay forum, not much attention given to it, but I am all for it.
Especially the engine part, if the engine takes a hit bad enough to cause the black smoke and the "Engine Oil" damage message, odds are you have some other stuff damaged as well, be it the ignition leads, fuel system, turbo/supercharger system, etc., and you should not have full power available. Radial engines due to the layout of the components are more durable and take more damage, but that's just life. Hit a Pony, Spit, or other liquid-cooled engine and the temp ought to shoot up unless you reduce power, where the radial will run a bit hotter, but not critically so. Hits in the P47 fuselage ought to damage the turbo and it's ducting, reducing available boost. Things like this would add to the "immersion level" I would think.
Hits to the wings and other control surfaces ought to detract from performance too, just as you stated.