As a regular commuter I disagree with this. 3 cars are clearly not enough when I've travelled at peak times. It gets incredibly packed. I don't mean to insult you, but there are also never any ticket checks done on those times (when I've been on) which may be why you would disagree as you won't have seen the overcrowding. It's awful at times.
In the daytime it's reasonable with only a few standing, sure.
I've had it so bad at times I've got off at an intermediate station and waited for the next train along (I know I shouldn't, but like I said, no ticket checks).
This is a prime route. With the distances between stops as well, something more like a voyager/meridian would do well.
Now I only travel Leicester to Birmingham and vice versa, mind.
Why oh why do people want Voyagers on this route?
A fuel hungry 125 mph unit on a route which is predominately 75mph. A unit which has less standard capacity and higher track access charges. Utter madness!!!
I worked the route for over 7 years and there's no way 5 cars 170's are needed most of the time. Whilst I don't doubt there's some latent demand I doubt you'd fill a 350 seat train most of the time, except perhaps Sat mornings into New Street in the run up to Christmas and the 0845 arrival into New Street in the week.
As for extending the Leicester terminators to Norwich, you'd need to rewrite the timetable. As it stands they would clash with the P'boro-Ipswich at Peterborough, the Liverpool-Norwich at Ely North and then the Cambridge-Norwich and Kings Lynn-London at Ely. Would also clash with the Norwich-Cambridge at Norwich/Ely on the reverse.
When XC were considering extending them to Cambridge every other hour the paths were pretty grim. 25 minutes Stamford-Peterborough, 25 minutes Melton-Leicester and 32 minutes March-Ely were some of the "highlights". Although they never ran the trains were shown in the Summer 2009 timetable. The extra platforms at Peterborough will ease the route slightly but Ely north Junction will be a challenge, along with the odd extra freightliner that now use the route.