I am unsure of the genuine benefits of 'time saved' for such a colossal amount of money spent.
The main thrust of the argument seems to be 'opening up the Northern Powerhouse' which is a term only a southerner with too much time on his hands could have conjured up!
The reality is that money and commerce will not advance northwards, and the notion that it is, is entirely without either evidence or merit.
The only result will be an even faster and more streamlined trip for money and commerce from the north to the south, thus increasing the status quo, and benefiting absolutely no-one north of Watford who actually has to suffer the consequences of this monstrous nonsense.
As you say, the supposed 'time saved' is a complete farce - because a lot of businessmen who will actually be able to afford to use the service, appreciate being able to settle down with the laptops and phones and get some uninterrupted work done - so the 'benefit' of taking twenty minutes OFF that time remains to be explained.
I believe it is nothing more than another ministerial ego trip, as was The Millennium Dome - and look how that ended up.
The money could be far better spent improving existing services, lengthening platforms, increasing and updating rolling stock, and sorting out timetables and maintenance - why would we want to add more to a railway system we already comprehensively fail to run in anything approaching a time-efficient and economical fashion?