I haven't had much fun in the endurance races.
You are correct, you would be very pi__ed if you raced for 2 hours, and only got 2nd. I got very upset after racing 2 hours, and on the last lap I messed up(badly), and could only get 5th place.
Some like the Super Speedway, and Test Track are kinda fun because they're SOOOOO easy, and you know you you're gonna win, unless something extremely bad happens, and you end up losing.
So, I guess they're kinda worth it thougfh, you get upwards of 100K to 400K for winning, and usually a car with a sell value of 250+ thousand credits.