For me, I cherish the heritage of the label = not worth a resub. I would like to get it reholdered but I would chance losing the vintage label. I asked CGC if they could maintain the label, and though they would try, they could not guarantee it would happen. If I have a keeper book, I just don't see the point of resubbing. It's still the same book no matter what the label says.
I agree with you the slab is part of the history of the hobby, but you could free it from the slab yourself and submit it as standard and save the slab and label - but why bother really - if a book is clearly undergraded that can likely be seen through the slab.