People in the seaside towns also want to get to Norwich.
Yes and I'm sure people from Cambridge change at Norwich to get to Cromer and Yarmouth... My point was the its not the middle of the country like Leicester so there is is less options for travel to cities from Norwich.
Always plenty wanting the Sheringham connection as we only have to be around 10mins late (normally caused by a late running EMR from Ely) and the connection risks being severed. Guards frequently announce for those asking for the Bittern Line of the good or bad news after Wymondham.
I suppose you wouldn't want to delay the Sheringham train by almost any amount lest the service going the other way has to sit around at North Walsham for ages. The woes of a single line. I have been on London trains arriving back at Norwich late where it's been announced that a local service is being held for us. Can't remember which one though, probably Lowestoft given the double track throughout.
We do hold some trains if possible but as you say, the single line sections do have consequences though with the new(ish) fleet recovering time is possible.
Leicester is not an important interchange unless you specifically are after MML destinations. Even then, Nottingham is just as viable via the EMR train at Ely/Pbo. You would surely just stay on the XC train a little longer for Birmingham to get connections to 'everywhere'. I'd imagine it's the primary interchange only for Sheffield or Chesterfield
No need to change at Leicester for those two - you could change at Ely instead to a direct EMR train.
Fastest journey is usually changing at Peterborough & Doncaster. That is followed by Leicester and then finally Ely. Each is approximately 20 minutes quicker than the next.
Is that true for both Chesterfield and Sheffield?
Yes the XC services on this route seem to do a decent trade all along the route.
Coming from Cambridge I generally prefer the change at Leicester to Ely if going to Chesterfield or Sheffield. The trains are generally better and the 158 trundle between Grantham and Nottingham coupled with 15 minute stop at Nottingham makes it tiresome. Also of course Derby can’t be reached on that train.