Abit drastic/impossible but lower the floor! To get rid of the silly step that folds out when you open a door, or just raise platforms where they stop. Mind you I would raise platforms at nearly all stations across the UK.
More realistically, MK4 coaches are built to a tilt profile aren't they? They're much more spacious inside. I'd strip the lot down to the body and rebuild the interior with as little unnecessary stuff as possible. I'd install more/brighter whiter lights and seat window alignment would be one of the highest priorities and more room in the luggage racks. Install a proper guards brake in a more suitable location than the 'office' with it's own door, droplight and emergency brake valve to replace the current 'office' making room for more seats.