My two cents:
If I didn’t have a 26-30 railcard then the railway would, by and large, be prohibitively expensive. And that’s with a full time job. From my point of view, a national railcard (of some sort, not getting into the specifics here) would be an essential part of fares reform.
Some Advance fares are too cheap. For example, I can travel from Liverpool to Manchester for £1.90 on a Northern advance, purely because they feel like sticking a middle finger up at TPE and EMR. For a 35 mile journey, this is just over 5p/mile - it’s effectively a free journey.
I can get from Birmingham to London for £4.60 with WMT - 2.5p/mile. Although there’s a significant time penalty & I recognise this pricing may be competing with the coach, I would still consider it good value if I were paying at least twice this.
These are the types of fare that under a nationalised railway, might be under threat. Yes, okay, we all love paying a pittance to travel but I can’t imagine that the lowest tiers of Advance fare, on a number of routes, will realistically survive.
On the other hand, many walk up fares are too expensive. I live & work in Birmingham and to see my friends in Manchester, an Off Peak return (before splitting) is £27.55 with a railcard, which I consider reasonable, or £41.80 without a railcard, over 25p/mile, which I consider over the top, especially given the horrendous overcrowding XC is famed for. Edited to add that under single-leg pricing, paying £13-£15 each way would seem about right.
And this may be controversial but I don’t think fares should be influenced by train length or capacity. If a section of railway, eg Birmingham - Cheltenham, is (in normal times) too busy for a couple of 4/5 car Voyagers to cope, then instead of raising fares to obscene levels to price people off, investment should be made in additional units to provide the capacity needed. No, there isn’t a magic money tree, but I’m of the opinion that there’s a lot of suppressed demand due to a perception that the railway is “too expensive” and furthermore, in some areas, “too busy to get a seat”.
So to answer the question, yes I’d be happy to pay more on the minority of journeys where I’m effectively getting a free ride, but on the majority of journeys, I wouldn’t be happy paying more unless there was investment to match.