It's difficult to see what you're getting at here. Perhaps you could avoid making such sweeping claims and grand assertions if your knowledge "isn't up to scratch"?
It is only my knowledge of London which isn’t up to scratch?
It sounds like you're talking about just railway enthusiasts to me, not "the population of this country". You're correct to suggest that enthusiasts get less excited about a very efficient mass transit railway than they do about country branch lines. However the former are the future of railways in this country and the latter are not.
I have heard many people who are certainly not railway enthusiasts have very negative reactions to news headlines such as an extra £4 billion of taxpayers money for Crossrail because it hasn’t opened when they are unable to use a train at all because the “branch” line serving the town where they live with a population of 5 or 6 figures has not been reopened. It may be the highly efficient mass transit system of the future, but it does give a certain sense of “one rule for London…” bearing in mind that 90% of the population of this country does not live in London and therefore will not be able to use it regularly, despite the unquestionable benefit it will have to those that will.
Nearly all railways are financially loss making, but I can assure you that the Northumberland line even now has a reasonably good business case. It's significantly better than the Borders Railway for example. Routes to the "middle of nowhere" as you put it, simply will not be reopening.
The Northumberland line once it reopens will serve as an efficient mass transit line for the City of Newcastle won’t it, because I’m sure some who are less informed would still describe it as a colliery branch line simply to lump it together with all others that closed. It is of course only reopening at all because it has been identified that it would serve a purpose today (or tomorrow).
The Borders Railway as I understand it suffers from issues of overcrowding because passenger numbers were underestimated in the original business case, even with 5 or 6 car trains and it only ends in the middle of nowhere because the English DfT will not allow it to be extended to its correct terminus of Carlisle, which would allow it to be used for LNER Tyne Valley diversions or even have a regular service to England, increasing efficiency on both the WCML and ECML when Newcastle - Edinburgh or Carlisle/Carstairs - Edinburgh or even Glasgow is closed.
I for example do not wish to see the S&CLER reopen through the middle of nowhere West Lancashire countryside, despite it being local to me because every conceivable journey that could possibly be made on it could be facilitated by reopening the Burscough South Curve and using existing lines, as well as providing a diversionary route to Liverpool, which represents a much more efficient use of funds.