The economics of fares and the worth to the individual will vary depending on a number of circumstances.
As far as I am concerned, as a person who travels intercity for leisure 95% of the time, I will deliberately pick dates and times which I know are cheap, and book well in advance. The premium in this case is not the issue - it's a predetermination that I want to travel in First Class and will seek out the most affordable fare to do so. I don't look at the Standard fares. I would not normally pay more than, say, £60 one way for London to Scotland, unless it's a sleeper fare in which case the saving on a hotel night might make me double that figure. My next First Class trip is VTWC to Liverpool, from Euston. £36.95 all in, with a railcard discount. That ticket includes lounge access and a cooked breakfast, as well as free wifi. I think that's a good deal and it is of no consequence that Standard fares might have been £7 or £10 on the same train.
However, I don't usually choose First Class on routes which don't offer freebies like food. A notable exception is SWT's 159 route to Exeter, which is long enough to justify me paying a small premium to guarantee a single comfortable seat and probably a nap.
On airlines, the First Class fare is usually absolutely extortionate - though I know a few ways to travel in First Class quite affordably, which involve looking at Business Class fare loopholes and using upgrade vouchers and miles. The product is not usually worth the premium in and of itself, though I am usually rewarded with bumper airline miles (think, "ah, now I don't have to pay money for those six short haul flights I was going to take later this year, I can just redeem those 40,000 miles"...). I also film the experience and stick the videos on YouTube and typically recoup the fare outlay with advertising revenue within 12 months.