It is interesting that EYERACE brougt up a reduction in entry fees as an idea to increase numbers. This idea was raised last year when CASC was looking to reverse the falling numbers in regional racing. For instance, lower entry fees, consideration for muliple drivers sharing one car over the weekend (instead of each paying full entry), some sort of refund if it all goes wrong early on Saturday. I personally had not heard mention of a sliding reduction in fees for those people who enter more events throughout the season (I think that proposal has real merit).
The result of all the discussion amongst the VARAC (vintage) group that I monitored was interesting. The veteran "established" crowd pointed out the reality that, compared to the overall financial outlay to go racing, a small discount on race fees was not going to make much difference. The new (and typically younger) members indicated that a reduction in race fees would be a significant incentive. So if you are trying to encourage new or nearly new participants, this idea may work? If you are trying to get the regulars to enter more races, maybe not?