Is first class in the UK really that much better, do you get your own rooms or something ?
It varies by operator but the good ones are very nice. It does seem quite different to First on the continent, I walked through a 1st Class coach on a Belgian train the other week and was amazed at how... like standard it was.
On FGW at least you get big reclining leather seats, loads of space, 'free' drinks etc. It is of course an absolute ripoff at walk on prices - £250 return to London from here, ouch - but booking in advance (Which I appreciate isnt an option for the OP now) means you can get some astonishingly good deals. It's almost always very quiet as well, I've been on trains where an announcement is made apologising for the overcrowding and I've looked up and the coach I'm in is almost empty. All for a few quid more than normal..
I hate traveling by train I'm always bored while in the car you can turn up the radio and listen to highway to hell and sing along loudly or whatever. Driving is more fun that staring out the window of a train or being bored on a lappy.
If the drive involves 100% motorway I find going by train more fun because I can simply browse the web or watch films. I will however only use the train if:
a) The drive is 100% Motorway
b) The train is direct and can be booked in advance at a significant saving
c) I do not need a car at the other end
I'll never bother if I have to faff about changing 2 times and standing around in random locations for hours on end, just as I'll never bother if the drive is interesting, but for going to places like London or the airport or something its awesome. Sometimes it sucks, if I want to get the girlfriends the route is completly pathetic and goes via Bristol and Wals taking 5 hours. It's less than 3 by car!
Don't knock it until you've tried it!