Scavenging? I doubt it. Production in 1944 was higher (by far) than any previous year of the war, yet this was the year of the heaviest bombing. There were more planes BUILT than they had trained pilots to FLY. The rates of production in 1945 were cut short, but had the year continued, it would have even left 1944 in the dust, for planes produced.
There was NO shortage of engines, planes, parts. Not on the whole. Maybe some localized here and there. Consider that well over 1000 Me262s were built, but only about 250-350 saw service. The rest sat parked until they were bombed. The 109 industry was broken up into many "cottage industry" sub assemblies. Even though this couldn't apply to engines, there were no shortage of the highest-power engines at the end of the war. Look at all the Ta152s made with high-power engines (granted, most were never delivered in time, but they had engines!). Look at the jet industry. It was hard to make those engines, and they used scarce metals, yet they made thousands and thousands of He162s, Ar234s, Me262s, you name it, they made tons of it, all while being bombed.
No, I don't buy that "spark plugs were scarce". I don't buy that at all. It doesn't seem likely (to me) given the pure abundance of hardware at the time. Given that it was such an easy switch, I have no doubt any squadron in a war of 1,000:1 odds on its own homeland would have switched the DAY they got authorization (or the plugs, if they didn't have them already), because it meant they had a better chance at surviving the day.
That's my interpretation of it.