Lv....XP to Next
30 641,774
31 821,471
32 1,051,483
33 1,345,898
34 1,722,749
35 2,205,119
36 2,822,552
37 3,612,867
38 4,624,470
39 5,919,322
40 7,576,732
TOT 32,344,437
Earning 32,344,437 XP to get through Level 30 to Level 40 would require approximately 1004 races in the 10 lap race at Indy in the Dream Car Championship, assuming that the XP reward stays at the current 32223 XP per race.
Say you average about 7'45" per 10 lap race, and unless I did something wrong here, I believe that this adds up to about 129.7 hours to complete the 1004 races required to earn all of the experience points needed to increase your level from 30 to 40. Quite a few hours, huh? The A-Spec auto grind method should come in handy I would think.
The stupidest thing about all of this is that you are only able to enter the Nurburgring 24 Hour Endurance once you reach Level 40 in A-Spec. If you manage to complete and win that race, I have heard that you earn over 9,000,000 XP, that simply go to waste. This race should have been made available at about Level 38 in both A-Spec and B-Spec.