I'm not "obsessed" about First Class travel - for example, I would never pay £17.25 (child) to travel First Class on the 21:07 from London to Liverpool when a £1.50 (or £3.50) Megatrain ticket is available.
The Standard Class Quiet Coach on that service can be very pleasant. I'd rather go and buy a £3 meal deal from Sainsbury's than pay £15 extra to travel First Class for a sandwich!
Generally, though, because I qualify for child tickets (and make good use of the Routeing Guide

) the difference in price between the two classes is minimal (in terms of the number of pounds, not the percentage increase).
I find that First Class travel makes train travel more appealing as a whole. (Quiet carriages, wide seats, plenty of legroom, clean toilets, tables of 4 to yourself, nice food, attentive service, peaceful First Class lounges, etc.)
When I go on my train trips, I wouldn't bother if I had to travel Standard Class. Travelling First Class makes the trips
much more enjoyable.
Having said that, my local "First Class" operator is Virgin - not Southeastern or Southern! London Midland is the other First Class operator round here, and I almost
never travel First Class with them! (Simply because Standard Class on 350/1's is good enough, and is almost identical to First Class).