You'd be surprised how many commuter types will choose which train they catch based on what they know may turn up.
On my local line, for example, there are most definitely commuters who have come to know which trains are booked for class 365, avoiding the class 317s/321s. Likewise many commuters are keen to know length information, both for choosing which service to use or avoid, and also as a guide to knowing where to stand on the platform. Particularly in the London area, there are locations where at peak times little details like knowing the type of stock likely to turn up on a given service, and therefore the precise spot where the doors should stop, can make the difference between getting a seat or not.
As for headcodes, again you'll find that there are quite a few displays at stations which show the location/headcode of trains. King's Cross has a number of these. They're primarily used for staff, but are placed in public areas, and are *very* useful for finding one's way to the train without having to wait for it to be announced, or for locating the incoming service. Plenty of non-enthusiasts use these.
The information may not be understood by leisure daytripper types, but I can guarantee a surprising proportion of non-enthusiast commuters would have some idea what the information meant, and would make some use of it.
