You wouldn't get far in a vintage car using the same oil as was put in the day it was built!
Tyres? Brake pads? Filters?
And compliance with current road laws?
If you want to start a museum, fair enough; keep it original (and probably unplayable). Museums are full of them.
But if you want a playing instrument, then use the best available new parts and rebuilding techniques to enable you, the owner, to produce the music you want, which, in my opinion, is the object of owning a concertina.
As for "devaluing" a concertina by restoring it, I assume you mean in a financial sense. Sure, some people will pay top dollar for "original" condition, be they collectors or players who want to have their new concertina set up by their chosen restorer.
However, I think most players, or would-be players, would prefer to buy a concertina that is already playable straight out of the box and would consequently pay more for such an instrument.
If the concertina is for your own playing use, it has no financial value for as long as you keep it; it is only when selling it that it acquires a financial value.
At least, that's my opinion....
MC