I wouldnt mind paying for a good league...
It 1) gets rid of wreckers/idiots ... they wont pay to do their thing and 2) provides a more mature atmosphere overall.
I've raced in paid leagues in other games (namely nr2003) ... no prizes (other than small things...nowhere near what the total entries come to) but it did provide a good server, consistent -enforced- rules.
One thing you should do for the league, as it was done in the one I raced in for nr2003, is require everyone have teamspeak or the like. No talking during races is allowed. However, admins can talk... This way, drivers can hide the chat windows, and admins can still give warnings, etc...not to mention people seemed to take warnings more seriously when they were verbal.
1 thing I don't think any league has done, is like corner marshals. I think it would be great if you have people spectating in the shift-u view, 4 or 5 of them per race, acting as corner marshals at various places on the track. You would also be kinda the "spotter" for wrecks. IE, let people know there is a wreck in t1, that there is a stopped car on the inside...and tell the stopped car to stay put, untill you clear them... I would love to do that, I spend alot of time spectating races anyways, I love to watch them as much as drive them.
I would pay for that... Hell, i would pay to spectate that as a marshall, just to see what kind of racing quality we could get.