I feel your pain, paddworth. To this day, the longest race I competed in a GT game was the Tokyo R246 endurance (the GT3 variant). This was 2:42:00 of gameplay for me. I fought through it all. And as much endurancing as I've done in the GT series, I know that others can't even make the time to make races happen. Play "Le Mans 24 Hours," assuming you own a PlayStation 2. You can save the game when in the pits in the Petit Le Mans and the 24 Hours of Le Mans (this year's race is June 18th and June 19th!). This can be very helpful for those who can't make the time to play the entire race. Then when you want to race elsewhere in LM24H, you can exit out of the game if you wish, and then simply reload your past save game. If PD implemented a similar system, it would make several inexperienced and non-dedicated GT racers feel very happy.
So let me personally chat with you all who are like paddworth with endurances. Endurance racing since GT1 have been progressively tougher. The oldest endurance in the Gran Turismo series is the Grand Valley 300km. While the graphics and cars have changed over the years, the challenge is the same. Also over the years, one other thing remains the same. Some can make the time to do endurance races, some cannot. I don't work or go to summer school, and even I cannot make enough time sometimes. I'm normally about sprint races. I don't back down from endurance races, though. Endurance races test your ability to drive for minutes even into hours. If you cannot find the time to do them or become intimidated by endurances, don't be. I'm not going to call you a wimp or bash on you because you won't compete in a long race. You have your strengths and weaknesses. I think endurances should be treated like Championships, in the sense that you can save your progress and continue on whenever you're ready. It would be tough to implement, but it would be great for many others because endurances can be reloaded so endurances can be completed without fail.
I would like to see this happen because as much as I like the Gran Turismo series, I want others to enjoy the series as much as I do, while work with strengths and weaknesses of other GT gamers. So, there you have it.