I would be against such an idea. All you have to do is complete them once and then you can just do all you wish good or bad...
IMO, the rating system in NR03 worked fairly well. Numbered ranks for each style of track (short track, speedway, super speedway, and road course) as well as a "Laps Per Incident" (LPI) ranking made people want to KEEP their ranks up.
Of course you had to work your way up from a lowly noob server, but once you got your rank up, pickup racing was great. You had serious people that wanted to race instead of crashers. The only time I had a problem with crashers was when someone had crashed / been crashed durring a racing incident and just wanted to retaliate, and when servers had no restrictions on them to people could get their rank up.
I would think this may be the best solution, but this is the only solution I've seen that worked so far.