I will give you a hint...it costs only 100 gta$ to run a race, there is no armor to buy, there is no ammo to buy, you achieve the goals needed to get the better mods on the best cars, you get plenty of cash and level quickly. I can make about a half mil in one 5 hour evening. So about 100k an hour.
Races are the best money makers now. I'm not a great racer but after an hour I'll have a 100k or more if I get lucky. Great RP too. My second character hit level 90 just from races and I don't trade wins or farm races (not judging, I did farm missions). The only negative is seeing criminal records and down the drain constantly. They're really overplayed. It's almost enough to make me want to drive backwards!
Personally i think adding an option in the race lobbies for "Repair vehicle" and adding a fee for using the Y button to respawn would go an awfull long way to bringing some balance and reducing some of the bumper car shennanigans.
I like the idea. How about exaggerated damage (realistic really) in races? One bad crash disabling your car or making it barely limp around would cut a lot of that out. It will hurt clean racers sometimes but you couldn't go full bumper car anymore.