Can you quantify that? Does it make any significant impact on the outcome?
Firstly rolling stock.
The current ex-tube rolling stock is over seventy years old, as was the previous ex tube stock. Even in steam days, the wooden bodied rolling stock tended to be super-annuated in comparison. This suggests that there is every possibility that:
a) The line can exist on a further batch of old rolling stock with a much reduced capital cost, or:
b) if stock is bought new, it can last the full seventy years, which means that you get around twice as much benefit for the capital cost.
Second, infrastructure.
From what has been said on here, the track hasn't had a proper renewal for some time (possibly before electrification in 68 ?). It clearly on a much longer replacement cycle than the rest of the network, so again, any calculation of the benefits of replacement track should take into account the likelihood that it will be in use much longer than elsewhere.