We have the benefit of the downgraded 1st class on our Northern service as we have the ex Scotrail 170's serving our local station. If I am off to Doncaster/Sheffield I will try and sit there as its 1.5 - 2 hours ish, if its just a local journey I dont bother.
Really there are different levels of 1st class, 'light' 1st class is a better seat, and a bit more room and 'proper' 1st class where you get at seat catering thrown in. Fare uplifts however do not always take account of this, I suppose its what the market will stand. I dont see any Northern services which would benefit from any level first class with the possible exception of Leeds - Settle - Carlisle but that would be to cater for the tourist market, and I cant see the economics of it working.
Really the majority of the Northern services are fairly local, our local service which is Scarborough - Sheffield is one of the longer at around 110 miles and 2h 45m end to end. In the summer you do get people travelling the full length, as people would rather travel without a change if they have luggage or are less mobile, you can save around 30mins to an hour by changing in York, but again not enough of a market to make it worth providing, and I suspect not many of those who do South Yorkshire - Scarborough on Northern would want to pay the extra.
What I used to find unpleasent was getting a 5 across seating unit on a longer journey but they seem to have disappeared from the longer distance services now