Yes, I agree that the evening "peaks" are now more like plateaus. But, in your example, the strengthening of the MC-Chester service is really the equivalent of an empty stock movement. What I was trying to get at was that (from a business point of view) provision for the capacity peaks should be as cheap and cheerful as possible, getting the most passengers into the fewest carriages. Because it is, by definition, "peak" provision, that capacity is going to be unused for much of the day. Now, on my local line we have 4-coach 333s. Off peak the service only really requires 2 coaches (in terms of passenger numbers - that would make the regular 2-coach service full and standing). So we have 50% of the stock that could be standing idle, but, instead, is running round the network picking up faults and the occasional chav, so is quite expensive. (OK, I realise that that 50% is actually spread out over all four coaches of a unit) As far as I can see, there are three approaches to this question of resource management:-
1) Hold surplus stock to be able to build or maintain peak capacity - for this approach the 142 is ideal, cheap in terms of passenger/journey cost. This is the traditional way, from back where we saw acres of full carriage sidings outside all major stations.
2) Use stock to the same expensive standard, offering peak capacity throughout the day, but encouraging greater usage off-peak. This is the model most TOCs seem to favour, but is vulnerable to the fact that off-peak travel is most frequently optional. As above, stock goes through the maintenance cycle with a large proportion of miles covered not earning revenue.
3) Using stock to the same expensive standard throughout the day, but massaging passengers journeys, so that the "peak" is much shallower and broader, so meaning you do not have to hold as much surplus stock. This seems to be the approach in, for example, SWT. The problem with this is that the window for cheaper, optional travel becomes squeezed, and the even cheaper season ticket becomes more prevalent.
I can see the merits in all three, and the place of a 142-type unit in the system