I am thinking that unlike more prestigious brands, this would really benefit from restoration. I have no idea what parts are available, but the moral dilemma of restored vs. unrestored original wouldn't apply as the value either way is not that significant.
So the same argument applies as in the case of restoring your dad's Morris Minor or whatever - you can get a better example for a fraction of the cost of restoring yours, but then you ain't got Dad's watch, just another watch. I presume he would very much like to bring it back to good condition.
In your shoes I (or your Dad?) would happily pay the cost of a restoration if parts availability makes it viable.
It'll be a great looking watch when done, that's a bonus!