I kind of have two point of view on this matter...
Firstly, as a rail enthusiast, I like to see locos out and about on passenger duties with LHCS. The rolling stock is normally more spacious, the seating more comfortable and just generally the feeling of being on a 'proper' train and not a mock-bus or mock-airliner style DMU. IMO Mk3s, with original seats, were the best coaches produced and are still going strong, although I have a particularly soft spot for GC's Mk3s

One thing worth noting is that there is actually a notable difference between 1st and std on a LH train, unlike many DMUs where the only difference is low density seating instead of high! I've also had my share of loco-hauled passenger trains, Fife Circle, Tall Ships Shuttles and GC Loco Hauled Replacements all came in front of my lens and I also rode on all 3.
However, coming from an operational perspective, the use of Locos and Coaching Stock on the modern railway is almost nonsensical in the conventional sense: a loco and a rake of coaching stock. The need for run-rounds at the terminating point adds to the time needed to turn the set round, older loco's reliability is lower, there is additional staffing costs associated with running a loco hauled service, slam doors aren't ideal and there is a notable increase in time lost when LHCS is dispatched compared to a DMU with power-operated doors. Take for example the Fife Circle, involving some sharply curved platforms. One station (can't remember which) saw the guard lock the CDL from the BSO, but then walk down to three seperate vestibule windows before she had a clear line of sight to give the driver the tip - all this after the carry on of ensuring that all the doors are secure and there isn't one on the latch. With a DMU it's a lot faster, close doors, close local door, 2-2 and away you go (in theory). The slam door problem is also evident with HSTs and Mk3 push-pull sets. However, these semi-permanent formations iron out a lot of the loco hauled problems pointed out above, such as the need for run round. In a way the NEXA sets and current HST fleet combine the best of both worlds: passenger comfort and some stock with a bit of history to it, with operational flexibility able to keep up on the 21st Century network.
So, I think what I've said there is that loco hauled is nice for the enthusiast, but isn't practical to the hard nosed businessmen of today's railway.