Most clubs that I have been associated with drop 1, sometimes 2 races for the points total. I think that is fair, and this coming from someone that hasn't been to the last 4 races!!! lol
I believe that dropping 1 or 2 races is all that is needed. You drop too many and you have to start going to who won more and down the line with seconds and third places to come up with a series champion.
Just my 2 cents.
Richard