The trains are poor quality because of their own mismanagement of the stock.
A 142 will always be a 142, with plenty of bouncy bouncy action, freezing cold draughts and heaters that will burn the hairs on your leg without warming anything else, sure. But look at what (the then) Valley Lines did with their 142s and 143s, compare it to the ex-Merseyrail 142s, and weep.
Similarly, when some of Northern's 156s were transferred to EMT, the latter stuck noticed up apologising for the poor quality of the trains. Essentially Northern Spirit refurbished them in about 1998 and Northern have done nothing with them since.
Given Northern are making profits of more than £20m a year, I don't think we can really argue that they're this poor impoverished operator doing what they can.
That is a fair point. Northern have been a lot better of late in this respect but its been a long time coming. Also, some units on other TOCs have had very useful extras such as tables fitted, which would be better when a 150, for example,turns up on a longish route.