Well, depends on intent.Looking at a possible resto project now. Was down at my mothers poking around in the garage and found this sled. Was a Christmas present in 1965 or so. Was going to refinish and restore but not sure I should. Sometimes its better to leave something in original condition, even if it is a little rough. Still trying to decide.
Do you want the memory, the function, or the resale value?
Definitely, for resale you only restore the structure and stablise deterioration. So you glue or weld things broken or split, use rust converter rather than grind any off, and oil or seal the wood rather that resurface it.
Only you know what suits 'memory'. But for function, all levels of refubishing including wood replacement if needed come into play. You simply keep to the original design.
You could also consider mixed purposes or intent.
But I'm sure you are already considering all this. Just hoping to contribute... -smiles-