That would depend both on occupancy and also on how much rakes the VB has. A 60% occupied 16 coacher VB is more useful than a 60% occupied 8 coached VB. Also, not to be neglected is the fact that VBs, atleast on some routes, overtake many daily trains that leads to slow down of them.
Case in point: GKP-ALD VB overtakes the GKP-LJN ICE which is 22 coacher vis a vis 8 coacher and carries nearly triple the nos of passengers when you factor in GN coaches. The overtake led...
more... to slowdown of ICE by 15 mins.
So, the question IR needs to ask is if it can't develop the infrastructure [read :new tracks, atleast triple lined sections] to run VB trains, what right does it have to snatch off hundreds of hours per day [a 15 min slowdown multiplied b y even 400 pax will give 100 hrs] from common travelers.