I hate to be glib, but these are so parochial / random / unimportant in the grand scheme of things - they would not do one jot to the government's perception or help the general public. I suspect they would be personally appealing to you
For political gain, let's think about gen pop, not us rail nerds...
>Sort out Euston scrum experience - (remove ads / bring back departure boards / announce platforms sooner)
> Better onboard food and beverage options (fun JP-style vending machines? - could also be on many platforms - there are ramen ones, good salad ones in US airports etc)
> Clarify connections like in Switzerland (screen in each carriage with platform numbers/times for connecting services at each station, including bus/tram)
> Simplify and standardize services to clockface, to same terminus where possible, to minimize conflicts/crossings (thinking South London multitudes or Manc Picc/Vic splits) - even if it removes perceived choice and seems unpopular, it will build usage. E.g. Hayes should be 4tph to the same place. Same with each route (2 or 4tph) through Wigan and Bolton.
> Cleaner, nicer, staffed stations with sheltered waiting areas, coffee/tea options, friendly staff.
edit bonus - every train should have wifi, that works in tunnels.... competition with cars and planes is the ability to be productive (or entertained!) -