Probably better to do one of the shorter ones over and over. There are lots of threads on XP per minute for all of the various races/race series. Find the ones that "pay" the best and do them.
Its the best way to hate the game. Do indy 500 over and over....
But I think you can do indy 500 with a controller, you put tape or something on the R2, you also need the X1 and you leave the car alone. It will follow the wall and the x1 is fast enough to win...
I have been doing the rubber band trick holding up the analog sticks on the indy 500 in aspec. You have to watch it to pit every 25 laps but the x1 wins easy even rubbing the wall. Can also do it on dream car indy. Takes 8 minutes, just hit the x button a few times to restart it. Did it last night 17 races while I watched a movie.
I like playing all the modes, but getting the points needed to get to 40 in aspec is not realistic.
The exact number I've read from someone who did it is 12 24H Le Mans races to get from 35-40. I'm at level 38 now and this seems accurate so far. I would guess 10-12 total if I didn't know.