"more than bare minimum" branding isn't about trying to tempt people onto the railway directly, but more widely about presenting a good image. If two candidates turned up for a job who were equally well qualified and interviewed equally well, but one was wearing jeans & a polo shirt, had messy hair and stubble, they'd make a less good impression than the other who was in an ironed shirt, smart trousers, was well groomed and had put aftershave on.
If the first impression people have of the railway "we're doing the bare minimum to get you from A to B" it sets that tone and clouds the judgement. If people get the impression that no effort is being put in, they'll view everything through that lens ("They didn't hold the connection for me, they clearly don't care"/"The trolley was understocked, they don't care about the passengers"/"The train was overcrowded, they just cram us in to rattly old cattle boxes"/"They put engineering works on the bank holiday and now I'm stuck on a bus") which eventually culminates in "I could take the train, but it was a bad experience last time so I'll take the car". That's not to say that a less bland sign solves all the issues and makes people only think of it positively, but it makes for a better first impression and changes the way in which subsequent interactions are perceived.
All that said, "bare minimum" does, sadly, reflect the railway in a number of situations so perhaps it's for the best that we just use white signage and black text. Whilst we're at it, paint the trains in battleship grey and rather than issuing train staff with uniform, just tell them "smart casual"