A Manton curve would not make much difference to East-West connectivity. It could provide a local service Wellingborough-Kettering-Corby-Peterborough but that's all, and would have to be justifiable on that basis.
But Peterboro' is a hub, with onward connections to Ely, Norwich and (yes) even Cambridge, which I'm sure would be mentioned in the reasoning, even if it is unrealistic for (say) Milton Keynes pax.
Bedford-Peterborough is about 35 miles on the A421/A1, but more than 60 miles by rail with a curve at Manton. The way to link Bedford with Peterborough by rail is at a Tempsford New Town ECML/EWR interchange.
A Manton curve would have no impact on what needs to be run on the Midland Main Line.
It would give for a connection into Corby once per hour, allowing for a current St Pancras-Corby service to be routed to Leicester (which was the OP to this little sub-thread's original suggestion, I think, somewhere up thread). I accept this would be subject to other issues.
The New Towns Taskforce first meeting was in Milton Keynes, the second was in Cambridge. They will be reporting next year. I shall be waiting to see what they recommend.
Agreed.
There are no funds for sops, only for infrastructure that facilitates new housebuilding and economic growth.
It would, of course, not be marketed as a 'sop'. There would be a lot of PR blah about "having extensively researched the possibilities for extending E-W services following the decision that a new line from Bedford to Cambridge not being economically justified, the decision to opt for an extension via Manton allows for multiple new journey possibilities and increased connectivity .... etc etc".
It could be made to look good, after all, most people have swallowed the EMR Connect marketing spiel-propaganda, which has essentially cut direct services between Luton, Bedford and Wellingboro to Leicester, Derby and beyond, services which have existed since the time of the Leicester and Hitchen railway. (Agreed, I doubt there were many back in those days, but that was for a very different era.)