OK my ideas, I've skimmed through most of this thread so sorry if they've been mentioned:
Multi-Class racing, have some in UF1.3 and some in UF1. Make it fair so there will be some UF1s in the field to race with, then you get the added skills of lapping the slower cars (which I presume they are).
Keep it to the short tracks, there's nothing more boring than being in a car that does a max speed of 90mph if you push it having 4 minute laps. There's not enough races held on the shorter tracks these days.
Run 2 races per round of equal length (20 mins sound good) at the same track.
Ballast - becoming much more common in motorsport these days, makes the racing closer and the championship much closer. Should run in BTCC style where the top 4 or 5 in the championship carry ballast through practice/quali and race 1, then race 2 the ballast is determined by finishing positions in race 1.
Drop scores: allow people to drop their 2 worst event scores. This also allows people a bit more freedom so that effectively they can miss 2 rounds and have a social life.
Also keep it to 1 night a week. Thursday nights are good, but personally I can't do them until mid-October.