Sorry, but Northampton - Bedford wasn't a "commuter" route when it closed. Very few people commuted between Northampton and Bedford in the 1960s and if they did a slow train (which took almost an hour) wasn't their way of travelling. Even now commuter traffic between Northampton and Bedford is limited.
Yes, but if you note what I wrote, I did say "low commuter flows" - and I stand by that. Mostly school kids and the odd worker and shopper to Bedford. And of course, there was the odd traveller.
But, I'm pretty sure, nobody would commute from Olney or Turvey to London - the train service just did not support ath.
And almost nobody would, say, travel from Birmingham to Bedford that way, even less likely, Birmingham to Hitchen or Stevenage. As you point out, it was very slow, and (I'm pretty certain), the trains rarely connected at Bedford (and Hitchen). My point is, it was very local, certainly with the poor service provided at the time.
Northampton - Peterboro wasn't "strategic" in any meaningful way, once beyond Wellingborough it served nowhere of any size - you can see that's true even today - between Northampton and Wellingborough the line ran south of the current A45 in the valley, beyond Wellingborough it ran north of the A45 and A605 to Peterboro.
Peterborough isn't, or wasn't strategic? OK, the line served Peterboro EAst, but it was, even then, a serious town, and the line continued to Ely (for Norwich) and Cambridge (and even Ipswich, though I'm not sure what the service was like back then.
It served a much more far flung set of populations - which would be potentially useful today. But truth is, not that many people wanted to use the service back in those times.
If you're heading from Northampton or Wellingborough to places further north on the ECML for example, it is much quicker to head north on the WCML or MML and change at places like Tamworth or Nottingham.
Today, for sure. But back then? I doubt it would be easy to go to Tamworth from Northampton, and then get a connection even to Derby (though I agree, if you only wanted to get to Derby, that would probably have been an option).
The only real "gap" in the Herts / Beds / Bucks / Northants area is one which was never rail linked to begin with - Luton to Milton Keynes - and there's no practical way to do that in any case.
Because there never was, because a) Milton Keynes was three houses, a church and cow shed in 1961 and b) even the Luton Bute Street to Leighton Buzzard line had a miserable service, usually necessitating change at Dunstable.
I can even remember a letter in Trains Illustrated (or possibly MR) back then about exactly this line - asking why BR did not run the trains on to Bletchley (as opposed to terminating at Leighton Buzzard) to give better connections into the WCML. Of course, there were v few expresses stopping at Bletchley then either.
For those that needed to travel anything beyond a train into the nearby town (such as Dunstable to Luton) it was the age of the car.