Nobody really uses the 2Cxx trains long distance (other than lost Cambridge tourists). Demand wise, they're really a KX-Stevenage and Stevenage-Cambs local joined together for operational convenience.
I’ve heard of a few people who will use them for journeys like Baldock, Letchworth or Hitchin to London to assure themselves of their preferred seat in declassified first.
In 365 days plenty of people used to take them as the first service to London such that they would always arrive at Hitchin modestly filled. With 2tph Cambridge to Brighton now I presume this is less prevalent nowadays.
My point about shifting 700s away from this service is more about making better use of the 700’s capacity though. This route is nowhere near crush loaded, and 700s could be more beneficially deployed elsewhere if through running doesn’t happen. It would need 16x 387 or 365, and in the case of the latter further platform extension work.
Incidentally, I've had time to expand on my earlier post regarding GN changes. I've copied and pasted below:
MONDAYS TO FRIDAYS
1) Minor retimings across the board, with Cambridge stopping service now departing KX at XX22 and XX52.
2) All the AM peak up Baldock to KX 365 services now call at Finsbury Park (I do wonder what if any operational logic there is to this, as one nice feature of the current timetable is pretty much everything through Finsbury Park platform 4 is non-stop, which must make life a lot easier for the signallers).
3) 1P07 0704 Peterborough to KX changes from 3x365 to 3x387.
4) 1P09 0714 Peterborough to KX changes from 3x387 to 3x365.
5) For those into rare track, 2x morning peak up services no longer cross over at Cadwell, however 1x evening service is now booked to do so (1P53 1942 Peterborough to KX).
6) The single morning Brighton/Royston and return service will run through to Cambridge.
7) 2C17 0827 Cambridge to KX omits Ashwell & Morden and Baldock. This is presumably to do with extending the Royston TL service to/from Cambridge.
8) 0942 KX to Ely increases from 8 to 12 carriages whilst 1012 KX to KX decreases from 12 to 8 carriages.
9) 2Y09 0602 Welwyn Garden City to KX changes from 700/0 to 1x717.
10) King’s Cross platform 0 seems to be out of commission, which has led to quite a bit of re-platforming at KX. This has led to some tighter turnrounds particularly for services which arrive or depart empty at King’s Cross before or after their respective service. Hopefully this may ease in the future.
11) 1R58 1957 KX to Baldock changes to 1954 in accordance with all the other XX54 and XX24 Baldock services, and calls additionally at Welwyn North as does the 2054.
12) 1R66 2154 KX to Letchworth calls additionally at Welwyn North, and is extended to Baldock.
13) 2R33 1256 Letchworth to KX now runs 4 minutes later as far as Knebworth with stand time at Stevenage removed (why this service ever ran like this is a mystery as it has always tended to leave Letchworth late by the looks of it, apparently being too close behind the Brighton service to get out of the sidings in time).
14) A new 1P80 0736 KX to Peterborough service formed of 2x365, which is a former ECS service converted to passenger, and calling at St Neots, Huntington and Peterborough only (however don't expect a sparkling run as it is booked on the down slow north of Woolmer Green!).
15) A new 2Y12 0936 KX to Welwyn Garden City service formed of a 700/0.
16) 2Y98 0140 KX to Welwyn Garden City changes from 700/0 to 1x717.
17) The various minor changes to routings and timings of the 2Cxx services in the evening made to accommodate the Moorgate services being diverted to KX are undone.
SATURDAYS
1) Cambridge to Brighton goes half-hourly through most of the day, as far as I can tell this is exclusively formed of 700/1, associated with this is a new 1C04 0603 KX to Cambridge.
2) 1C76 0032 KX to Cambridge runs 1 minute later and changes from 1x387 to 700/0.
3) 2R72 0024 KX to Letchworth changes from 700/0 to 2x387.
SUNDAYS
1) The hourly Cambridge - Gatwick Airport service is extended to Brighton except for one trip at the start and end of service.
2) 2R42 1632 KX to Letchworth changes from 700/0 to 1x387, and 2R46 1732 KX to Letchworth changes from 1x387 to 700/0.
The outstanding elements compared with the ill-fated May 2018 timetable are thus:
1) Weekend KX-Cambridge stopping service to extend to 2tph between Royston and Cambridge (is this still the plan or has this been permanently changed to 1tph reversing at Royston?).
2) Horsham-London Bridge and KX-Peterborough to be joined on Sundays.