Let us at least get away from the fiction that maintenance, and in fact renewals (as in like-for-like renewals) are somehow "investment" in the railway. Even ministers sometimes spout this nonsense from their civil service brief. They are not investment. They are just part of the continuing cost of maintaining a steady state. Investment is about additional capital features, new flyovers, additional mileage of electrification, that type of spending.
Let us also SUBTRACT from the value we are getting any features taken away. Every resignalling etc scheme seems to reduce the provision of emergency crossovers, etc, which is then a confounded disbenefit whenever they would have been useful but no longer there.