Surely these new big screen machines are just asking to be vandalised, it's like leaving an unattended plasma screen TV on the platform.
Personally I find these big screens a bit overpowering when you are stood right up in front of them. It isn't natural for the eye to trace along such a big amount of space at such close range.
Screen technology isn't that expensive these days to be honest, though they should maybe split the screen in two so that one half shows timetables / train information whilst the other offers the ticket purchasing facilities.