Scott,
I agree.
Those 30 Amp fuses, almost certainly, were not put there by accident. There was load that was blowing the correctly sized fuse.
In my opinion, one has to assume that the loads that caused the 30 Amp fuses to be installed, ran for some part of the 70 years that the house has been there. There may not be the same load connected now, but, IMO, one has to assume an overload ran for some amount of time.
Until proven otherwise, the existing overfused branch circuits are highly suspect as potential ignition sources.
