Many times low level races get uninteresting when you have unlocked later races and thus you wont go back as often. Maybe this could be countered by chaning the payout structures:
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Beginners: 20k Cr/15 Minutes
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Semi-Pro: 50k Cr/15 Minutes
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Pro: 100k Cr/15 Minutes
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Expert: 175k Cr/15 Minutes
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Master: 250k Cr/ 15 Minutes
This way it doesnt matter what events you are doing since all of them payout rougly the same amount. This could lead to a much more enjoyable endgame and a better usage of all content (not like GT7 where you have to grind 1-3 Events to get money)