GAMEPLAY MECHANICS IMPROVEMENTS:
1. Introduce multiplayer tournaments, mix classes, cars, tracks and skills. If not let the host change the race in a ranked race because even if the players are good (and are having fun) racing gets pretty stale fast. Do the same for club races. Most people we meet in club vs. club races are rammers but there are some who are great players and it's just a shame we can't change the challenge when we are bored with it.
2. Let non-competitive clubs get their XP somehow as well. Be it in 'Follow the Leader' or 'Keep your distance' just add something like time constraints (timer, or a ref time) or a minimum distance required to travel to obtain an XP award, otherwise those challenges are more of a chore to do than anything else, and my guess that wasn't your initial intention. That will surely make them more difficult too, but better (or ANY) rewards for the challenge should compensate for that.
EDIT:
@CLR: Thanks, I'll be sure to read the guildines next time. But when I saw the topic and the opportunity to let Eden know (via official channels) in what ways players think they know how to improve their game just made me so excited that I jumped into writing without giving much thought about limitations Diablo had put on us. :P I feel like nfscu2 of TestDrive Central now (I think you should get the reference).
BTW, I deleted the post between CLR's two in order not to clutter things up, so his post is not a double post.