I bet that every driver (even Kimi) would gladly drive F1 for free if they would only have to come for the race-event. And they could just leave straight after that, in privacy without anyone knowing you/paying attention to who you are. (Though the teams would have to pay for the flights etc. No one can afford doing that forever without getting money.)
Believe me, it would get really boring for everyone of you just to drive alone around the track for hours. They did do that when testing was allowed and I've heard so many of them saying that they were bored to death after a while.
I remember the interview when Alonso and Webber were interviewing each other and both talked in a way that they'd be glad to skip Friday completely since it's so boring.
I don't know if this is going slightly to off-topic. Kind of not and kind of yes.
Jan Lammers (in F1 between 1979 and 1982 and again in 199?), once told in an interview that he often was dizzy from the amount of laps he drove in practice. The races itself seemed short in comparison....
But I don't agree with the rest of your assertion that drivers would drive for free if it were just the races. I think that, despite that F1 is not as dangerous as it used to be, racing is an extreme attack on the emotions. It really takes a lot out of drivers, to trust their lives, their bones and marrows to the car and with that, to the people who have built and prepared the car.
Niki Lauda describes this very well in his autobiography 'Protocol'. If the team puts pressure on you, if as a F1 driver you don't trust the people you work with, if you feel that you are being used as a monkey in a space-program... then the motivation to race disappears.
I find the similarities betwee Niki Lauda's last year at Ferrari - he stopped the 1977 season two races before the end - and Kimi's situation at Lotus comically similar. Both had health issues that were bearable... but not in combination with the relationships as they were in the team.